Define GL Account For Reason for Movement

Hi

In Migo, our users scrap articles using movements 551/552 together with a specific reason code.  The GL account differs depending on what reason code is selected.  I need to change the GL account for one of these reason for movements, but cannot see exactly how to do this.  I can see the account modifiers in OMJJ and GL assignment in OBYC and have run a simulation in OMWB, but it looks to me to relate to the movement type and not the specific reason code.

I am quite new to this area and would really appreciate some guidance on how to change a GL account for a specific reason for movement.

Many Thanks

Simon