How do I update a UDC when it is in use?

I've got a (user level) UDC which may be in use by several users.
I understand that a setcatalog command can be used to "point" the
users to another file; however, I don't know who has it set and
who doesn't use the UDC at all at each of many sites.

Options:
1. Build some elaborate command to pipe  listuser command to a
file then parse and setcatalog to a new file?

2. Kill all jobs and sessions then update the original file?

3. Find out if a command file can override a UDC?

I would prefer to use command files to replace UDCs.

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