Or, you play by the rules and your old code continues to just work. Might not be optimal, but at least it will run. Your customers will thank you . . . well, we all know they won't, but they won't be speculating about your ancestry in public forums.

I don't remember how many Mac applications were '32-bit clean' and ran without modification when VM was turned on. I do know that some apps had to do significant rework, and that there was a whole generation of abandonware where developers didn't think it was worth the effort and just walked away from their customers.