Hi,
Please check PR release strategy with release indicator as "can not be changeable" can fulfill your requirement. Refer the thread:PR line item deletion issue
If the restriction is user specific, you can check the option of transaction variant. Create a transaction variant in SHD0 for ME52N and deactivate the deletion button. You can activate the variant globally or to specific users also, if required. You can also maintain the material, short text, account assignment and item category fields as non-editable in the variant, so that the user can not add a new item. Refer the doc: http://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/40d1443e-0184-2c10-c68d-c612f771fe6f?overridelayout=t…
Regards,
AKPT