Complex scenario for re-billing counter readings

Hi Team.. here is another scenario to try to resolve:

Suppose we have a monthly usage base and the pricelist for the reading usage item is set at $32 Each

We read January, February and March the following

January - 5 - $160

February - 10 - $320

March - 3 - $96

these are being billed the first of the following month.

Then we discover that for the customer, the price should've changed to $30 at the end of February.

I know the easiest way would be to go to AR and create a Credit Memo for the difference ($96 - $90 ($30x3) = $6) and reprice the contract with the new price attached to the pricelist