I originally perfected Multi-Etch® for titanium production. It’s a nonacid (pH 6.8) alternative to hydrofluoric acid. I’ve also tested it on other metals with great results.
You can clean iron contamination from platinum without removing any platinum ions. I’ve done limited testing with Multi-Etch® on platinum for etch effects—that is, removal of platinum ions—and there doesn’t seem to be any effect. I have not tested it with rhodium plating but I assume there would be no effect on that either.