in the worst case, it will grow back. it doesn hurt the dog, but you cant just do it any time, theres a time when the hair will easily come out (but still need a little tug) and a time when it may hurt. without seeing the dog i cant help you! its a bit like when it moults.
just found this site, its a border terrier but the principle is the same
http://www.emblehope.co.uk/border-te...-and-grooming/