Material Replacement button in Purchase Order

Dear All,

My question is quite related to this question, there the author wasn't satisfied with a system behaviour, but i'm facing with some problems. Normally I can create a PO reffering to the contract and PR, but after pushing the "Mat. Replacement" button, then clicking the "Material Replacement" tab,then choosing "Other Material Numbers" the part of the data is copied from the first line (such as Outline Agreement,Contract Item, etc), but the fields Purchase Req. and Requisn Item, Requisitioner become grey and uneditable. In order to save the PO after this i must specify these fields.

Unfortunately, i couldn't find the desirable settings in SPRO myself. Would you please to tell me (or give the link) in details in which section of SPRO i can find the necessary settings or maybe...should i search for Z-code solutions?

Thank you for your attention.

Best Regards,

Alex