There is such function 'SplitStackInto'
As i understand it should be used with custom merchant handlers, but it is useless if it doesn't call container onInsert scripts like it MoveItemToContainer does.
"Calls the item's unequiptest and unequip scripts, if any.
Calls the container's canInsert and onInsert scripts, if any.
Calls the item's original container's (if any) canRemove and onRemove scripts, if any."
Please add it