The grille on the Ashdown 1x15 cab I used to own was held on with velcro and could be prized away from the baffle with a screwdriver. Even if you're only using the Rumble as a power amp and cab', I'd still be surprised if it will be much of an improvement on what you already have.
I'd question whether the BF 1x10, whilst very loud for its size, would do the job for you. A single 10, no matter how capable, just won't shift enough air to be adequate in a rock band. It'll be expensive to find out, too.