... (in my experience and others' I've read here) 
inevitably there is damage to the paint on the 
cel that you are prying off and paint left 
sticking to the cel underneath.  If the layers 
are seriously misaligned to the point that it 
compromises the quality of the image, then it may 
be worth it.  But my experience (with a $15 cel 
that was not near to my heart) was not 
encouraging enough to make me try it with a cel 
set that I really cared about.

Sometimes you can pry apart stuck layers by 
probing gently with the corner of a photograph 
(image side down).  But don't push your luck if 
it looks as if the paint is starting to come. 
loose.