BADI/user exit for me22n - disable/grey out field quantity (MEPO1211-MENGE)

Dear all SAP gurus,

When changing PO (ME22N), I need to disable (grey out) the quantity field on item (MEPO1211-MENGE), when all scheduled quantity is already received (EKET-MENGE = EKET-WEMNG).

Have tried using LMEIGICJI and Handle_event method in CL_SCREEN_VIEW_MM. But still doesn't go to the screen that wants to be disabled.

Tried using BADI ME_PROCESS_PO_CUST, but couldn't find how to disable the quantity field.

(IF_EX_ME_PROCESS_PO_CUST~FIELDSELECTION_ITEM only works for custom field).

Please kindly advise

thanks in advance