I have "successfully" separated stuck layers in 
the freezer. Once as an experiment with two cels 
from the same sequence stuck back to back, and 
once because the layers of a cel I liked a lot 
were stuck horribly misaligned (I bought it that 
way), and it was only worth a lot to me if that 
were fixed.

I put the word "successfully" in quotes since 
there was damage to the paint in BOTH cases, even 
though in the second case the damage was so 
minimal you'd have to know what you were looking 
for to be able to point and say "that's it". In 
the first case, the damage was more severe, even 
with reminants of a stuck sketch on the back of 
the top layer helping things along. In the second 
case, the cel wasn't stuck very strongly yet, to 
the point that it started to come apart on it's 
own with a tiny tug.

Note that the damage seemed more from the process 
of separating them, than from the freezing, as 
far as I can tell. . . But I don't know what the 
results would have been if the cels hadn't come 
unstuck, because I did have to dry condensation 
off them.

So bottom line is: No. If cel layers are stuck, 
then just leave them -- anything you do to try to 
separate them again will damage them!! But if you 
absolutely HAVE TO separate stuck layers, then 
it's an option to consider and is potentially 
*less* (note the term "LESS") damaging than other 
methods. But the cels have to be only VERY lightly
stuck or have something else helping you separate 
them, like the reminants of the sketch paper on 
the first one I tried.

Many Sharp Smiles,
--Drac