Can we set tolerance limit in Sourcing and restrict to change supplier on PO document?

In negotiation during award quantity can increase or decrease. We want to setup tolerance limit as same quantity or within tolerance limit quantity. Quantity at PR RFQ and PO Level must same. At PO also we can be able to change supplier and quantity.

Please assist us to do setup for tolerance limit in Sourcing and restrict to change supplier and quantity at PO after purchasing document creation from RFQ.