auto default item purchasing category on PO

Hello,

we have a requirement to default purchasing category on PO after the PO has been created.  On schedule maintenance procurement team review item category and updates however the PO already created with item wont reflect the updated category.  Is there is way to default the category on PO updated on item?  we are in process of upgrading to 12.2.7 and noticed in 12.2.7 the category field is non editable.  This cause us a impact on our procurement process.

regards

Madhu