I've heard a shocking amount of variants on suggestions of bombing/drilling volcanoes to set them off early & prevent damage so here's my thoughts on the subject-
I'm not sure of the logistics of it, but I'd imagine it would be a very difficult, expensive, dangerous & probably a hit & miss process if it's possible at all. The question is 'when could it actually be justified'? If a volcano is certain to erupt soon, it's probably too late to take action, and if it's not, then how could you convince people that it is worth doing, when the volcano may not even erupt naturally within anyone's present lifetime? I'd imagine people would be more inclined to wait it out. Another problem would be liability for damage- If a small eruption is set off with a bomb which unexpectedly causes a lahar that swamps a town (even if evacuated as a precaution), every resident will hold the organization involved responsible and they'll probably have to pay out millions if not billions to all affected.