Hi Robin! I've listed some helpful sites for you. Good luck to you!
Thanks for the references!
If just at edges, can you caulk?
I would stipple plaster using a paint brush to repair the wall while leaving a textured finish. Follow up with stippled (not brushed) paint.
I would hold a piece of cardboard in the corner seam and dab textured paint on the wall using the cardboard as a protective shield for the clean wall.