Hi,
As per standard, there will be no accounting document generated in case of returns
You can check in PGR, there will be only material document and no accounting since the return stock always posted to the Quality and after inspection it will be posted to Own stock using 453 movement type
In case of 453, Material document as well as accounting document is generated and this value will be updated with the value of your new price as per standard
In order to acheive your requirement, you have to take the return stock to sales order stock using 657 E movement type. This should happen before your material master price updated with new. After that even if the price update in the material master your PGR will be posted with the sales order locked price which culd be equal to PGI price
Hope it is clear
regards,
santosh