How to fix black gloss paint bleed on brilliant white eggshell walls + paint stripped from walls
First rule of masking the wall when painting trim - you need to paint the trim like there is no masking at all.  With practice you can learn how to paint a good enough line that you don't need to mask at all but until then the masking is for protection for an &quot;oops&quot; it is not carte-blanch to just slap the paint on the trim plus all over the tape.
I suggest you use a razor to razor the black paint off the wall.  Then mask the black dado and use a artists' paintbrush to cover the areas that you scraped off the white paint.
spackle is for drywall so yes you can use it to fill dents in drywall.