In message , Tim S
writes
Perhaps an orbital sander might blend the paint edges in enough. Otherwise
lining paper would be the normal solution.

Need to be wary of doing this if the house is old, possibly lead based
paint.
Have you enough spare new paper just to hang a piece and see how it turns
out when dry? Unless the paper is really thin and fine, I wouldn't normally
imagine paint on plaster would show through.

Cheers

Tim

--
Clint Sharp