No grant that i know of to change it from commercial to residential. You would qualify for the vacant homes grant of 50K if you left it until it was vacant for 2 years but you wouldn't qualify for the additional 20K derelict home top up unless you can get a report from an engineer / architect stating the building is unsafe and needs to be completely redone. Check with the council about the building in question before making any moves though.
Regarding the planning permission, I don't know the answer to that, but I'm going to follow it up as I'm considering doing something similar to you at the moment and it's the planning piece putting me off.