The fare difference WAS-KIN vs. WAS-PVD is $2. If you're looking for a cash/credit card refund, they'd probably take 10% of that, leaving you with $1.80 (or you'd get $2 credit towards future travel). I'm not sure whether that's worth going out of one's way and arriving up to a half hour early. Depending on how busy the station/ticket window is, it's probably not worth the ticket agent's time either, if they could be helping someone else.
If I were traveling, I'd just hop off early and eat the $2 difference. Others may feel differently, but that's what I'd do.