I had the 70 mph speed limiter removed from my MK6 at the dealer cost me £75+vat. Like you said I had to give written permission for them to remove it and produce the V5 to prove I owned the van. It never fried my ecu so can't see that happening. Can't see any problens as all they do is plug it in to IDS and turn the speed limiter off. 5 minute Job but they'll probably keep you waiting 1/2 an hour
It will only wipe the map if they update the pcm.