I ream my cobs all the time with a cheap butner. They don't always stay quite round, but it increases the capacity once in awhile.
You can use alcohol on cotton tips and pipe cleaners in the shank, but not in the chamber. The cob is pretty absorbent and you might be building a conflagration.
I've got a couple of estate cobs and they're great! I once bought a group of used cobs, early on in my pipe smoking, and not only got one that was unsmoked, but for about $10.00, I got 2 others AND a wonderful Kiko block meer that looked 'cobbish'...That meer made my day!