Protect name of an entity pin

So your case is a perfect example for doing this type of thing. I have made clock assignments to muxes in the past, and don't remember the name changing, but it's a little funny. You could try the "Implement as Output of Logic Cell", and I think that should work. Probably worth making a test case though.

Also, you could make your assignment a little more generic if the name changes, i.e. when applying the clock constraint, apply it to something like [get_pins mux*]. That won't be the exact syntax, but play with the Name Finder in TimeQuest to get it right.