Is it possible to prevent a newer SVN client (say 1.6) from automatically upgrading a working copy that was checked out with an older client (say 1.4 or 1.5)?
I find that as soon as I touch a working copy with a newer client, anyone using an older client to work with the same files can no longer do so (for obvious reasons).
Assuming requiring everyone to upgrade their SVN clients isn’t an option, is there a configuration setting or flag I can set to prevent my newer client from making this change?
Andy’s answer is misleading — there is nothing wrong with using multiple client versions on the same repository; the problem you’re describing arises when multiple client versions are being used on the same working copy.
So unless the same person is using multiple clients (which could certainly happen, e.g. command line client + TortoiseSVN), it shouldn’t be a problem to not have every person upgrade their clients.
To directly answer your question, no it is not possible to prevent auto-upgrading of working copies, but it is possible to undo it after the fact. See the release notes for a Python script that will accomplish this.