No, you don’t have to strip off the poly right before painting. (Fortunately. That could be an enormous discomfort.) In case the coating is rather shiny and slick, I'd personally sand the doorways flippantly initially just to make sure the spackle has some thing to grip. The DecoArt stain blocker http://kitchencabinetpaintersnea65319.blogs-service.com/27650145/rumored-buzz-on-kitchen-paint-colors-with-honey-oak-cabinets