Pulling the rug would mean revealing that your company never really owned the copyright, so at the very least you make yourself look bad.

Also, I don't imagine courts take a favourable view of transfers of ownership which are essentially fraudulent. I'm not a lawyer, as you can doubtless tell, but I presume it wouldn't be good for you if they could prove you'd planned the thing from the start.

There's an analogy outside of copyright: stolen goods. Sale of stolen goods isn't a legal transfer of ownership, but you don't want to be caught knowingly selling stolen goods, much less proven guilty of it (and the whole point of 'pulling the rug' is that things play out in court). I presume a similar principle would apply with intellectual property.

But since the project is under BSD license, they could make a case that they are allowed to use your changes (under that license). I'm not sure how that would eventually play out in court, though.