Re: RG 750 Stud broke and surprise to change it.
It should be easy to break loose with pliers, although I'd use channel locks. You have plenty of grip at the top of the stud with where the break is. WD40 will do nothing but wick under the paint and into the wood. If you can't break it loose [and i'd have that edge protected with thin cardboard or thin wood trying], you'll have to cut the paint away 1mm past the edge of the anchor and use a cats paw, or whatever you have that will work to pull the anchor.
And your other anchor is not seated, and it should be. That may be a previous botched repair if it doesn't just pull straight out.