“FF is off by default on consoles” (that’s pretty much a quote from the Fragworld interview with Badman and Bongoboy).
This implies it’s different for PC’s. Obviously, if you are running your own playnow server you can set it up however you would like. There is a big question as to how campaign servers work on PC and who will be running them (many clans won’t bother running a server they’d seldom get to play on). My guess is FF will be off by default on most campaign servers run by hosting companies.
I like the idea of accepting the buff but not really being able to use it. You sort of palm the thing like a magician 
The disguise thing is difficult, there needs to be some what to discover the guy, but doing that by test firing at him is kind of weak. Granted, an operative can disccover another operative, so maybe this is enough, Once discovered by the other operative he’s “psotted” for everyone. That plus getting close to the guy who you stole the disguise from (makes perfect sense, hey, that’s me over there!) I wonder if it would work if these were the only two ways to discover an operative?
hmmm, say you can’t discover* him by probing fire (even FF on you just shoot at the guys legs), then in addition to the two ways above the only other way would be noticing he’s not taking buffs?
*that’s not saying you can’t kill him, if you were sure he was an operative you have to be able to kill him after all, you just don’t get any enemy hit indicators. Of course, this wouldn’t work with FF off but maybe there’s some work around for FF off situations.