Basic Customization > User Interface Customization > Adding Actions and Hooking Them Up in the UI > Action Framework for Windchill Client Architecture > Action Customization Guidelines
  
Action Customization Guidelines
It is important to note the following:
If you have an <objecttype> element in the custom-actions.xml file, and that type exists within another actions.xml file, then actions from your custom file will be added to the full set of actions supported for that type (defined in the actions.xml file).
This custom-actions.xml is read last of all the actions.xml files, so if action names are duplicated, the one in this file will be used
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If you have a <model> element in the custom-actionmodels.xml file, and a model by that name already exists, your model will completely override the ones processed before your custom action models file. Be very careful in the naming of your models so that you do not wipe out others from files read in prior unless that is the intent.