It is like buying a cherry mid 70s Porsche 911 and then slapping a turbo and a wing on it and giving it a paintjob. It can a) never be undone, b) everyone who ever owns it in the future will know someone screwed with it, and c) people in the future will not get to enjoy it do the same degree that we have.
Thinking "well, it's a gift, it shouldn't be sold anyway" means virtually nothing. I doubt the groomsmen are planning on outlasting the cameras, which means likely 50-60 years down the road, they will be owned by someone else. Film is already in a precarious position. I don't think it needs beautiful jewel-like cameras with JERRY LOVES MARY carved into the sides.
Doing it to a Canonet is one thing, but doing it to the Rolleis and doing it to Leicas equate to fairly similar violations in my book.