Return item with different promotion

Hi All,

We are using Xstore version 15.0.0..549

We are dealing with next issue, please see below the scenario :

- customer wants to exchange for a bigger size an item bought last week in promotion Buy one get 2nd half price, the price will be $15 / item (regular price $20)

- customer will return the item and will take a bigger size under same style, but the style have this week promotion 40% off , for same regular price the item price will be $12

So in the end for an exchange done for an item bigger size under same style we are losing money $3.

We cannot delete the promotion for the new item scanned in on transaction.