I love it when people test things and report their results to the community. That makes this a nice hint.

Now, is "Anonymous" willing to test what happens when the UID/GID of the imported home folder already exists for another user on the destination system?

exactly. UID/GID is much more important in the grand scheme of things.

Well there are a few things to be aware of:
1. The users short name does not exist on the target machine (otherwise you would obviously overwrite an existing homefolder)
2. If there is another user having the same UID, then the copied folder could be read/write by this user (if he knows that this folder exists, otherwise he won't care of). By the time you create a new user with the same short name as the copied folder, then this new user gets a new UID on this system. But as Anonymous mentioned OS X is smart enough too see, that there is a conflict ans solves it without any hassles giving the existing folder the correct user permissions.

Regards,
Claudio

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- claudio