I don't believe that IDPA has an exact weight for trigger pull in the rule book. the best I can find is "Internal action work may be used to enhance trigger pull as long as safety is maintained" I think as long as the pistol can be safely fired it should be fine but if an accidental discharge happens due to too light of pull I get the feeling you won't be allowed to compete. ever!
IIRC in USPSA production class it is 4 lbs of pull required. Granted I have never had a trigger pull test done at any competition.