Originally Posted by
pdlamb
The normal way to remove a frozen bottom bracket is to soak it (sometimes for weeks) with penetrating oil.
It's not clear to me why you need to remove the BB to replace the derailer; it'd probably be easier to soak the derailer mounting bolts with penetrating oil.
Shimano c101 type, it doesn't clamp on to the seat tube, but rather has a bracket that is attached to the BB.