Enhancement of Released PO layout Question?

Hello All

I am meeting a issue of the layout of the released PO enhancement.

The released PO have two ways for opening in change mode:

1. Almost fields can be change after the PO approing

2. none of a field can be change after the PO approving.

But I want control some field, such as price, payment terms and currency etc to only display by open in change mode.

Can I use this BADI ME_PROCESS_PO_CUST to satisfy this requirement? Or you have some good suggestion for it?

Best Regards

Gerry Li