UID and GID cannot be changed once created.

An existing user/group could be destroyed and recreated to make such a change, but it should be possible to simply change the number.

Granted this leaves files with invalid ownership, but that can easily be mitigated by searching for the old UID/GID and updating them to the new. This could be an automatic or optional step performed when making the ID change. Alternatively, point to instructions on how to perform the change manually or simply display a warning to indicate the issue.

This is of particular importance for builtin users/groups, which may conflict with a user/group on another network or even that existed prior to the builtin being created by FreeNAS/TrueNAS.

For background: I opened because I have an existing user/group that conflicts with the builtin user/group that TrueNAS creates. They have the same name, but differing UID/GID. The incoming PR (7523) for that proposes to "fix" this issue will rename my existing user/group to append a number to them. These user/group entries actually predate when they were introduced by FreeNAS/TrueNAS and I consider this change to be kinda hostile.

It seems to me that a better fix would be to allow changing the UID/GID of the builtin user/group.

This would allow better integration with other systems that also have that same user/group and UID/GID.