I'd say there's small but real chance that a shop might mess it up if the mechanic hadn't done many. But any reputable shop should be able to handle it.
Is this a job any LBS worth their salt should be able to do?
Definitely. I've chased the threads on BB shells many times, albeit on new frames, and I have absolutely no formal training in such things. Any competent bike mechanic should be able to do it.
I doubt you'd be keen to buy the BB tap set as they are ££££. If ever there was a LBS job, this is it.