I think, as long as you take every reasonable precaution - so liberally greasing the tap and only cutting maybe a turn to a turn and a half before winding it out, cleaning down the flutes and applying new grease, maybe also blowing out the cylinder with a long nose blowgun (one which gets right into the cylinder so the air blows stuff out rather than a short reach which will be inclined to blow stuff into the cylinder - make sure the valves are closed before blowing so the bits come back out the plug 'ole not onward past the valves!) assuming you have the luxury of a supply of compressed air of course - then I don't think you should worry too much. Although it would be wrong to say I've done hundreds of thread reclamations like this - from just running a tap down the hole to correct a minor bit of damage to installing a helicoil insert - I have done a fair few number of them over the years. In fact I've done more inserts on small engines, Briggs and Stratton, Tecumseh, and others as the side valve jobbies have very short reach plugs which are easily stripped if over tightened - the combination of short reach plug and "ham fisted" horticultural worker/gardener is almost guaranteed to give you a regular supply of engines with these problems! I can honestly say I'm not aware of any of the repairs I've done later resulting in an engine with bore damage - and a lot of the horticultural ones will be engines I saw regularly over a year or two for servicing. I'd argue you're more likely to end up with this sort of damage because you don't properly blow out the road grit from around the plug before removing it at service time. If you don't know what I'm saying here then you should always slacken the plug by half to one turn, to loosen up the packed down grit, before thoroughly cleaning around the base of the plug and cylinder head - compressed air works best for me - It's sometimes surprising the blizzard of grit which can get in your eyes if you're not careful. If you don't do this then some of it is bound to drop into the plug hole as you remove the plug and almost certainly get down between the piston and cylinder wall. Many modern engines will have individual "coil on" ignition coils and because of the way the coil often has a rubber seal/grommet between it and the "tunnel" in the head, are much less prone to this problem, but I still tend to give then a blow out just in case - doesn't take any time at all, so why not? also, with a lot of engines now being twin OHC with the plugs in the middle between the cam covers, you can get oil leaking down around the plugs if there's a gasket leak. Quick "squirt with the air gun quickly reveals this and stops the oil dumping into the cylinder if you haven't noticed and just whip the plug out.
So I think my advice is, exercise good practice, don't rush the job and don't worry - it's almost certainly going to be Ok. For the inexperienced a far bigger problem is going to be inserting the tap without cross threading it! Due to poor access or weirdly angled plugs. The FIRE engine, for instance, has two plugs angled slightly one way and the other two angled the other way. I believe this alone can cause a newcomer to the engine to cross thread the plugs/plugs.
