I repaired a small patch (50p) on SWMBO's Corsa a while back after the body shop had been careless with the tape (or using the wrong type).
Did my best to get a clean edge by flicking off the loose bits with a finger nail - being careful not to go to far of course. Didn't rub down much beacuse of the risk of changing the surface of the paint underneath and it looking different once lacquered.
Cut a hole in a peice of card to match the patch and used that as a handheld mask (held an inch off the body I find this gives a more feathered edge, so cutting back is easier). Sprayed several light coats over 1 hour, then cut back with some 1500/t-cut a bit later. Sorted - the "edge" of the original lacquer didn't show at all - turned out mcuh better than I expected. Body shop were prepared to do the whole rear wing - my fix was less hassle than arranging to take the car back in (especially as this would have involved re-doing a special edition stripe - that I didn't think they'd be able to sort properly).
Now - 156 Turismo
Gone - Merc C240 Sport (RIP), numerous VXs, MGB