good receipt posting for Interchange material

hello

i have interchangeable part 4711 (materialtype HERB) and 4712 (materialtype ROH)

for 4711 i have a schedule Agreement. pos 1 is 4712 with dummy qty of 100 pc

and pos 2 is 4711 with the correct order qty. MRP type is PD.

after good receipt posting to this schedule Agreement to pos 1. 4711 the GR-qty is reduced the SA for 4712 after MRP run.

How the SA for 4711 can be reduced immediatly after GR-posting ?