if you reference an outbound delivery, then you get the goods issue quantity as proposed quantity in MIGO.
Whenever the proposed quantity is different from the quantity that physically arrived, then your receiver should switch on the protein computer and think about this situation instead of overwriting the proposed quantity right away.
if you want restrict him, then you need to check the quantities in
MBCF0002 Customer function exit: Segment text in material doc. item
EXIT_SAPMM07M_001