Not sure I agree on making it BoP, hear me out cause it doesn't effect me at all, just trying to see all sides... I think if your current Phantom chest guard isn't bound, the new one shouldn't be either, just to cover the "holding it for a friend" aspect or all the people who bought cartel packs after seeing what these things were going for on the GTN (doubt they'll sell quite as well now), there would still be some loss incurred otherwise. Really, an even exchange of the item in question with some kind of credit voucher for mod extraction costs would be the most comprehensive (if complex) way to go about this. Yes, they'd be injecting a little more creds into the system, but no more than say, the money we got in lieu of recruit gear.
Edit: Or, heck, let us eat the extraction cost, if someone's got their end game mods in, they probably have the credits to get them back out again.