I seem to recall that if you can have an ability sometimes, that's good enough to get a feat, but the feat is only active while you qualify.
For specific example, you take the brawler rage power, which makes it so you have improved unarmed strike while raging. Could you then take improved grapple(which would only work while raging)?
It is just the only case i can remember it being adressed. The problem is when you qualify for the feat less than a minute a day and leveling is done in a vaccume withou buffs i dont see hoow he can qualify as far as pfs is concerned.
But short of scowering the books the stuff on temporary bonuses is all i can remember.
Ah, found it:
Some feats have prerequisites. Your character must have the indicated ability score, class feature, feat, skill, base attack bonus, or other quality designated in order to select or use that feat. A character can gain a feat at the same level at which he gains the prerequisite.
A character can't use a feat if he loses a prerequisite, but he does not lose the feat itself. If, at a later time, he regains the lost prerequisite, he immediately regains full use of the feat that prerequisite enables.
It doesn't say you need to have it permanently. Since you would have improved unarmed strike, you would qualify to nab things that require it, but said things would only work while you have improved unarmed strike, turn off when you don't, and turn back on automatically when you do.