Enable Goods Recipient in me22n

Hi Expert,

I have requirement to enable Enable Recipient field in me22n -> item-> account assignment -> Recipient based on some condition.

I have tried with me_process_po_cust FIELDSELECTION_ITEM with below code .

FIELD-SYMBOLS: <flds> LIKE LINE OF ch_fieldselection. LOOP AT ch_fieldselection ASSIGNING <flds>.
    CASE <flds>-metafield.
    WHEN mmmfd_recipient. "its recipient (553) 
       <flds>-fieldstatus = '.'.  

 ENDCASE.
ENDLOOP.

But its not triggering for standard field.

Thanks in advance ,

Anupam