All joking aside i could see a makeshift primitive weapon, but anything more it would take a techpriest of somesort and from my understanding the very idea of las-pistol made like that would not only be heresy but an insult to the cult mechanicus.
I think it depends entirely on where you're from in the universe… Yeah your standard imperial worlders are likely to not even bother monkeying around with the insides of any tech device but then you have you're Fortress worlders that are a little more familiar with how a basic Lasgun works and might be willing to ask for a Machine Spirits forgiveness to save their life in a pinch by using a device for something other than it's intention… Then you have people like Death, Feral, and Feudal worlds… I assume they could really give a **** less about the Machine Spirit unless a ranking member of the Mechanicus was scrutinizing them, and even with their utmost care he would be livid about their disrespect for the tech. Also think about it like this, would it be a greater sin to alter tech or to wholly allow it to be destroyed?
In game terms all you really need is Tech-Use, Survival, or Medicae as they are the major crafting skills, I would say to make little makeshift object then these skills if posessed would be enough but if you were trying build production lvl weapons and armor then you would need one of the trade skills, a full shop, and an ample amount of time.
I play a Macguyver Catachan and he blew up an Ork gargant with an appropriate amount of explosives… the problem was our group didn't have a detonation device, which meant one of us was gonna have to stay behind to blow it up. I volunteered and used a 20liter water jug, a bucket, rope, and a rudimentary pulley system to craft a detonator for the explosives and managed to sneak back to my squad as they were watching the detonation and saying their hearfelt goodbyes. And if we would have had to vox-caster I would have scrounged a detonator from that too.