I have no formal training in legal issues, so this might not be worth much...
By disassembling the code you create an intermediary copy of the code. Courts have found this to be illegal (MAI Systems v. Peak Computers)!
On the other hand, courts have excused intermediate copies for certain reverse engineering purposes on the grounds of fair use,
for example to to reverse engineer an interface
(Nintendo v. Atari and Sega v. Accolade).
So I guess it's a question of wether what you do
constitues fair use. (To reverse engineer an interface has been basically established by the
courts as fair use. The DMCA gives other exceptions
but I guess your case is not covered.)
But maybe there is another area of law that "overrides" IP law (Online Policy Group v. Diebold).
Boy, you need good legal advice...not mine...;-)