Leaving primed grenades/explosives anywhere else than in the inventory than the hands makes maybe not so much sense. By allowing modders to adjust this, balancing a mod would also be easier, as spamming pre-primed grenades sometimes can make things very easy.
I know there is isExplodingInHands, but I think that can be a bit much.
So I would suggest an option to not allow putting primed explosives (or to prime explosives) in certain inventory slots:
invs:
- id: STR_BELT
allowPrimed: false #default is true