There's a lot of stuff like that that you can probably get away with... but I'm not sure it's prudent to try it on valuable production data. If it breaks your database nobody is going to have any sympathy for you.
FWIW, I can't immediately think of a reason this would cause a problem, at least not on 9.4 and up which use MVCC catalog scans. If you're really still on 9.3 then it's notably more risky. In any case, I've not had any caffeine yet today, so this doesn't count for much.
Ah, 9.3 is not using MVCC for system catalogs?... Ouch. Then most probably it is really not a good idea. That said, I am not modifying table names, only index names... and I guess the internals, the planner etc. are not working with names, but with oids instead?
