Being that the svn boook recommends deleting a branch after merging it into the trunk with the reintegrate option, is it safe to revert the mergeinfo property changes for that branch that are added to the trunk?
Our trunk now has many mergeinfo entries for old branches that no longer exist.
I do not understand where these entries would ever be used at this point.
It'll be 'safe', in that you won't break the repository or your working copies or any future functionality.
But I like the idea of keeping them, simply because you could in theory go and work out who actually did a particular piece of work and what its real history was (in theory, if you cared enough). If you delete the merge info, you no-longer have any hint where the associated code came from.
However, it's a weak argument for keeping this info if it's getting out of hand and causing issues, or even if it's just annoying you.
Perhaps you could keep it for a couple of revisions then get rid of 'old' ones. That way, a blame will turn up the merge revision, which will also allow you to find the associated merge info as it was then.