No, not directly to a FLA. And you can't edit a SWF directly, either.
You can get utilities that can 'decompile' or 'extract' parts of the SWF - including code - so that you can build it back up, but they have an obvious hacking implication and cannot be discussed on here. If you are legitimate in your intentions, it shouldn't be hard to find one of the many available through a search engine.
A couple of months ago I let it be known I had one. You wouldn't believe the number of e-mails I got asking about it.