Can I lvl 5*s without affecting scaling?

VizMantis

I'm not ready to start pushing a 5* transition, as I only just got on firm footing in 4* land. That being said, I've got a 3/1/1, lvl 255 OML that I've been using to clear the easy nodes in pve. It'd be nice if I could toss him some levels without messing with my current scaling. So how high, if at all, can I push him (or any 5*)? Is it as simple as keeping him under my highest lvl 4*?