If you change system UDEs, you must always apply those changes when migrating to a new release.
In general, I would not change the system UDEs, but create my one ones, which is much more update safe.
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You need to update the ude file for NX. You could be using the one defined in your configuration (usually resource\user_def_event\ude.cdl) or it could be one attached to the ISV machine.
I agree with @Stefan_Pendl if you modify the out of the box files, you have a maintenance chore with every upgrade. I would create a separate cdl file, and include in fron ude.cdl. Take a look at how we handle the Siemens UDEs.