I would think soaking in water would do it.
You unscrew the detonator and use boiling water to melt out the body explosive. You remove the blasting cap from the trigger mechanism then screw the inert trigger into the inert body. EZ Peazy.
“ I would think soaking in water would do it.”
You would think incorrectly. What use is a grenade that would fail to go off if the soldier had to wade through a stream?
I don't think so. The main charge is TNT, which doesn't dissolve or absorb water. The firing mechanism is sealed, and is ignited by a percussion cap when the safety grip is released.
A grenade must remain fully effective in all battlefield conditions; and, those can be pretty wet. Those babies will detonate under water.
The striker mechanism can be unscrewed from the grenade, at which time the TNT can be melted and poured out. The detonator can be drilled through and then submerged in water. If memory serves me, the cap can be unscrewed from the striker and the primer removed. That primer is just like a "large rifle primer". Tricky trick, that one.