First - this should be posted in the Amps section. Not a big deal, but more "amp" folks likely to see it there. It'll probably get moved by a Mod.
In any event, as long as the one cab's ohm load is not below your amp's mininum ohm load, you're OK. Simply put, just let your ears be your guide as to volume and overdrive. When that happens, it's time to back off on something, more than likely, volume or bass EQ. As long as you keep that in focus, no damage should happen.