Yes you can unpledge at any time. I don't think powerplay has any effect on faction ranking. As for if it's worthwhile or not is a matter of some debate. If you want to make money then you need to pledge to Hudson or ALD to get the bounty bonus. Rank 2 with either gets you a 50%/40%/30% bonus depending on your powers standing 3rd/2nd/1st. Rank 5 gets you a 100% bonus. You get the bonus twice, once when you kill the ship and again when you redeem your vouchers at a control system (i think this is a bug). So an initial 200,000 kill ends up being around 600,000. With rank5 ALD i'm making roughly 15million an hour, sometimes you get a good run and make more other times less. Of course you to maintain rank 5 you need to around 5350 merits a week, fastest way to do this IMO is killing ships in crime sweep zones, you get 10 merits per ship destroyed regardless of size. This could take 5-6 hours depends on whether you get a few good runs where you're part of large group of ships that are all targeting the same enemy at the same time. The time spent doing this is just about covered by the 50m weekly rank5 bonus payment you get. When the Cutter is released and the double bonus bug is nerfed then to be honest i believe you'd make more money trading smuggling Imp Slaves in the Cutter.
