No MRP based assessment after GST. Tax need to be paid only on transaction value on every supply. MRP under LML act may indicate the final price of the product and it no way connected with taxable value of supply under GST. The question of abatement does not arise so long tax is paid on transaction value.
Under sec 15 of GST act the value of supply is the transaction value subject to the recipient should not be related and price is sole cosideration.What the amount you are getting for supply is the transaction value.your internal transfer price subject to above is Transaction value under GST.