Hi,
OMW9 is for FI trasactions only. I forgot to mention it.
Now, for your requirement, no need to add MIGO_GR in OMJJ allowed transactions, since MIGO is already there for the movement type 501. If you want to change the accounting document type for MIGO-GR, just add the new document type against MIGO_GR in OMBA - Goods Receipt
Regards,
AKPT