It would depend on the design of the riser as to the possibility of "lengtheing the limb bolt hole". The process of doing this to a bow's riser would be a very tricky task and doubt if anyone would want to tackle it. The diameter of the drill must be smaller than the threads of the tap and I'd bet that you would damage the original threads while trying to maintain proper alignment necessary to avoid damage. Damaging the original threads would mean using a helicoil to repair it and if the riser wasn't wide enough to allow the use of a helicoil,,, you'd be SOL
