I guess what you mean is rebinding to
another management class.

You can rebind all active files to another group 
by the method you describe.
You will fail to do so for 
inactive fails - they remain 
unchanged.
After this process, next expire process will
expire your files according new (B)
managemnt class.
If B defines less file version or shortet times 
to keep data, then there will
really some files be deleted, otherwise not.

However, if your aim is to
move data to another storage pool, this will not happen this way.
You are only able, assuming you have co-located storage pools,
to identify volumes (tapes)  with data concerned and issue 
MOVE DATA command so to move them to storage pool of your wish.

Do not worry, none of such changes will 
impede your restore abilities.

And - if you are not sure - do simply a test before,
create small test backup bound to (A),
let it be rebound to (B), etc..


Bye
Juraj SALAK