Could a monster, say a Dragon with the Snatch feat, still use Snatch if it shrank in size? If it became a large or medium creature, such as with a Polymorph spell, and that creature still had bite/claw attacks.
Snatch is: "Prerequisite: Size Huge or larger.
Benefits: The creature can start a grapple when it hits with a claw or bite attack, as though it had the grab ability. If it grapples a creature three or more sizes smaller, it squeezes each round for automatic bite or claw damage with a successful grapple check. A snatched opponent held in the creature’s mouth is not allowed a Reflex save against the creature’s breath weapon, if it has one.
The creature can drop a creature it has snatched as a free action or use a standard action to fling it aside. A flung creature travels 1d6 × 10 feet, and takes 1d6 points of damage per 10 feet traveled. If the creature flings a snatched opponent while flying, the opponent takes this amount or falling damage, whichever is greater."
It comes down to the prereq being something that you need to just take the feat, or it being what you need to use it as well? I think it would still know how to grab with its' bite/claw, but the rest of the feat would probably not apply.
Presumably, if the creature no longer satisfies the prerequisites of a feat, it can't use it again until it does.