Jeff Ishaq wrote:

Thanks for the tips, folks. I'll try both the putty knife and the
masking tape approaches, and let you know how it goes!


Please do!

After all I was just taking a wild stab at the problem, but it makes
perfectly good sense to me!

After all, with a "spackled wall" (Eww!) I think it would rather
difficult to make even the BEST tape lay flat and keep the paint from
seeping/bleeding under it, so as to leave a nice, CRISP edge!

But, if you WEDGE the Putty Knife into the corner enough (Not enough to
bust the you know what), and carefully apply the paint and PULL the
knife away and INTO the wet surface....Wooo Hooo!

It's "got to work" with some "experimentation"!