If an NPC shows as "neutral", you can often get them back to "friendly" with a bribe of some sort. Money usually works, or sometimes an item (make an offer they can't refuse
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Of course, if you then try to steal again, well, I don't guarantee they'll stay friendly.
When I was doing the shoplift/pickpocket stuff, I always saved before making the attempt, and restored if my thief was caught. Boring, but safer.
Nightowl2