I was surprised that after long search and considering the extensive modding documentation of OpenXcom and particularly the Extended version, there's apparently no mention on how to change the damage ranges of both regular weapons and explosives against terrain. The only reference I have is from the wiki (25%-75% for normal weapons, flat 50% for explosives) but no idea of where these numbers are actually stored or if they are in fact hardcoded even in OpenXcomExtended (which I doubt).
My goal is to make explosives better at demolishing things and reduce the ridiculous damage of the blaster launcher without sacrificing its ability to break UFO walls.