Adding new line to approved PR

Hi,

PR with one line qty=1, price = 10, approved and PO created and paid.

PO qty = 1 and price= 5.

Encumbrance is at PR level, so the used amount is 5.

Now business want to modify approved PR and will modify line 1 to price = 5 and will create another line for qty=1 and price = 5.

PR will follow approval cycle and after approval line 2 will be added to a new PO using AutoCreate process.

1- Is this doable ?

2- Old PO will not affect due to this change

Regards,

~Syed