Build new operators out of processes and bundle them into extensions as follows:
Create a process with the operators you want to wrap using as many input and output ports as you want your custom operator to have.
Go to File > Create Custom Operator and specify the appearance of your operator as well as the parameters.
After saving as many custom operators as you want in some new folder, go to Extensions > Create Custom Extension to bundle them into an extension.
Configure your extension and specify the folder containing the saved custom operators.
The finished extension is stored in your .RapidMiner/extensions folder and loaded on restart. Install additionally the Rapid Development extension to (re)load without restart.
You can share your extension with others who also have the Custom Operators Extension installed.

Version 1.1.3:

• Fixed broken connections on AI Hub in case of special port names.

Version 1.1.2:

• Added Text Parameter Macro operator to define text parameter types with text type and template text.
• The defining process of the custom operator now gets the logverbosity of the process containing the custom operator on execution.
• The defining process of the custom operator gets a random seed depending on the random seed of the process containing the custom operator on execution if the custom operator was stored with version 1.1.2 or higher.
• Added a new Save button to the Create Custom Operator dialog which saves in the original location if an existing cusop file was opened or the Reload from file button was used. The old Save button with the Repository Location Chooser is now called Save as...

Version 1.1.1:

• The ports of custom operators can now be given names on the last page of the Create Custom Operator dialog.
• Added Throw Custom Error operator in order to throw custom errors from custom operators.
• Added a generic Dictionary connection with encrypted values and a new Read Dictionary operator that can be used to read the dictionary values from inside custom operators.
• The Category Parameter Macro operator has a new parameter 'set as integer macro' that sets the macro value as category index.
• Process files bundled into a custom extension via the Repository folder can now be executed with the new Execute Process from Custom Extension operator.
• Added Repository Location Parameter Macro operator to define Repository location parameter types.
• The Create Custom Extension dialog has a new Load from File button to load an extension definition. Every extension definition is stored in the config subfolder of the Custom operator folder and double-clicking that file opens the Create Custom Extension dialog with the extension definition loaded.
• Fixed capitalization of custom extension names.
• Removed support for Studio 9.3.

Version 1.1.0:

• Added possibility to define custom operators with subprocesses using the new Custom Subprocess operator.
• Added option in the Create Custom Operator dialog to define a parameter as expert.
• Added Integer Parameter Macro and Double Parameter Macro operators to define integer and double parameter types with min and max value.
• Added Metadata Helper operator in order to fake metadata for scripting operators that have no metadata.
• Fixed the force dependencies calculation for subfolders.

Version 1.0.1:

• Compatibility with RapidMiner X
• Added Previousbuttons to the dialogs.
• Added the possibility to store visualization config json file for Use Case Module Custom operators
  • If the custom operator type in the Create Custom Operatordialog is set to use case module, Visualization config json files needs to be provided for each connected inner sink port of the process
  • These visualization config json files will be stored in the created custom extension
  • They are used in the ISGAT service as the default visualization of the Use Case Modules
• Fixed a bug for double typed parameters, which are used as custom parameters. The default value was not correctly set.

Version 1.0.0:

• Added the integration of use case module operator in case the Data Structure extension is available
  • If the Data Structure extension is available during startup of the Custom Operators Extension, the functionality to create Use Case Module Custom operator is enabled.
  • The custom operator type can be set in the Create Custom Operator dialog.
  • If the type is set to use case module, Data Schema objects (created by using the Create Data Schema of the Data Structure extension) need to be provided for each inner source port of the process.
  • These Data Schema objects will be stored in the created custom extension.
  • A Use Case Module Custom operator is adding Adjust Data to Schema operators at the start of the inner process.
    • The data assistant functionality (see Adjust Data to Schema documentation) can be used from the Use Case Module Custom operator to adjust the user data to the required data schema.
  • If the parameter Force dependencies is selected during the creation of the custom extension, a dependency to the Data Structure extension is added as well
  • If an extension with Use Case Module Custom operators is loaded, but the Data Structure extension is not available, these Use Case Module Custom operators are not available (the standard ones are still available).
• Added dialog page to describe the ports of the custom operator for the Help and add a tutorial process.
• Added possibility to specify a folder of additional icons (as png) to Create Custom Extension dialog.
• Added dropdown for extension name in Retrieve from Custom Extension and Open File from Custom Extension.
• Fixed custom operators depending on others being broken in some cases.

Version 0.9.9:

• Improved responsiveness for custom operators with big nested processes.
• Repository files can now be bundled into a custom extension via the Repository folder and be opened with the new Open File from Custom Extensionoperator.
• Repository folders (formerly IOObject folders) can now have subfolders.

Version 0.9.8:

• Custom operators are now put into the same subfolders as in the repository and can be reordered inside those via dialog.
• Custom operator ports now also appear without automatic validation.
• HTML tags can now be used in the custom operator description.
• Fixed error when custom operator port delivers no data.
• Fixed wrong self-reference in some cases of a custom extension created with force dependencies.

Version 0.9.7:

• Added dialog page to reorder the custom operator parameters and make them optional/mandatory by clicking on them.
• Added option to define parameter dependencies for custom parameters.
• Added dialog to specify the order of the operators in the custom extension.
• Fixed attributes parameter not working as custom parameter anymore.

Version 0.9.6:

• Added option to hide the defining processes in the Create Custom Extension dialog. Note that since the hidden processes cannot be inspected on error it is recommended to add an error handling using the Handle Exception and Throw Exception operators in the defining process.

Version 0.9.5:

• Removed the requirement to have a jdk installed on the machine and internet access for building a custom extension.
• Drastic speedup for creating a custom extension.
• Added two new operators, Total Custom Progress and Step Custom Progress, to defined the progress of a custom operator.
• Added two new operators, File Parameter Macro and Directory Parameter Macro, to help create parameters in custom operators with a file chooser looking for a file with a special ending or a directory.
• The order of the parameters of a new custom operator is now defined by their order in the .cusop xml.
• The Create Custom Extension dialog now allows to specify an extension icon out of the standard icons.

Version 0.9.4:

This version requires RapidMiner Studio 9.7.

• Custom Operator definitions (.cusop -files) are now stored in folders in Projects or (non-Legacy) local Repositories. By storing in Projects the versioning can be used also for Custom Operator definitions.
• RapidMiner objects (IOObjects) like ExampleSets and Models can now be bundled into a custom extension and be retrieved with the new Retrieve from Custom Extensionoperator.
• New custom extension without the feature from the point above still work with version 0.9.3 and RapidMiner Studio 9.3 to 9.6.
• Added right-click option to create temporary custom operators to allow a preview without having to build a custom extension. These temporary operators stay around until restart or until they are overwritten by another temporary operator with the same name.
• Added Reload previousbutton to the Create Custom Extension dialog to reload the last input information.
• Fixed metadata not working in some cases where the custom operator had no input port or when context macros were used.

Version 0.9.3:

• Added Attribute Parameter Macro operator which sets a macro to an attribute name that can be selected from a dropdown. 
• Fixed the metadata for parameters that select attributes: Now the metadata is taken from the custom operator port that is directly connected via first input ports. If no direct connection is possible, the Attribute Parameter Macro operator can be used.
• Added a Reload from Filebutton to the Create Custom Operator dialog that allows to reload the information from existing .cusop files.
• Added the option to define which custom parameters should be optional via checkboxes in the Create Custom Operator dialog.
• Fixed the automatic (re)loading not working with the Rapid Development extension for certain custom extension versions.

Version 0.9.2:

• Added integration with the Rapid Development extension to load custom extensions on the fly 
• Minor improvements to Create Custom Extension dialog

Version 0.9.1:

• Added the possibility to bundle additional jars into the extension.
• Added two operators which help to create parameters of custom operators: Boolean Parameter Macro and Categories Parameter Macro.
• Added the option force dependencies to store the extensions used in the defining processes as required dependencies. This allows to automatically install the extension dependencies when installing a custom extension from the marketplace. This is not recommended when distributing the jar file since it prevents loading the custom extension if not all dependencies are there.