If you don't want to change the PO, then the GR will be evaluate all received stock with the PO price, when you then post the invoice (which is for 100 instead of the 130) then you will see a difference and SAP will distribute this difference to the stock in case it is still there, resulting in a change in moving average, if already consumed then the difference is posted to a difference account.
It is convenient but can result in big fluctuations of your price, sometimes even in errors, and the consumption is done with the wrong valuation if it happened between GR and IR.
Better change the PO or post the excess unplanned without reference to keep it under control