Multi-version .macrhi

Unfortunately no, they are not a thing. In fact, I just wrote a reply that might be helpful in explaining what Rhino for Mac attempts to do.

Another alternative, for Rhino 7 onward, would be to distribute using the Package Manager, which does support version- (and platform-) specific packages. Not much help with Rhino 5 and Rhino 6 though, I’m afraid.