To rename a custom data you must have all files with instances of that type open when you make the change, otherwise they will be considered to have a different type with the old name when they are next opened. Do you mean the UUT process model data type? I would recommend against changing that since you will make your custom version of the process model less compatible with the default version, especially since the end user/operator does not necessarily ever have to see the type name, so it's probably not worth the hassle in that case.
Hope this helps,
-Doug
