A320:
a) You cannot benefit from feats for which you do not meet the requirements, independent of what those requirements are or why you no longer meet them.
(If this were to happen in a campaign I ran I would ask the player if they wanted to have the character revert, and if they decided to keep the change, I'd probably allow them to replace that feat, but that would be a ruling mad in my capacity as DM.)

b) No, the prerequisites are the same, unless a new version of those feats have been published, or if the new entry explicitly calls out that it counts as an older race for the purposes of requirements. (I seem to recall hearing something about the new version of the Duergar being its own race, but having a feature that makes them count as dwarves for the purpose of requirements.)
As a side note, a lot of new races do qualify for the Squat Nimbleness racial feat, as that has the requirement of being EITHER a Dwarf, OR a Small race, and I know that quite a few new races have Size: Medium or Small, chosen at creation.