You are the HJ of a Modern PPTQ. At the beginng of round 2, you ask your floor judge, James, to help you in a deck check. While doing the deck check James asks you “What do you think about this card? Isn’t it marked?” and he hands you an altered Blood Moon. The art of the card has been extended to the borders making the card distinguishable when the top of the sleeves are facing you. The card is marked and can’t be played, so you ask the owner of the deck, Andrew, to replace it with a non-marked one after explaining him he has committed TE-Marked Cards. Andrew will be assessed a Warning for his infraction.

Andrew doesn’t have a replacement for the Blood Moon but chooses to play an Island instead, and you fix the deck list to match the current deck. At the end of round 3, Andrew finds you and tells you he’s traded for a non-marked Blood Moon and wants to play it instead of the Island.

What do you do?

Judges, feel free to discuss this scenario on Judge Apps!

[expand title-Answer]This week’s scenario was inspired by a recent update in the IPG.

Additional Remedy
If the player is unable to find replacement cards, he or she may replace those cards with basic lands; this change may be reverted at a later point if replacements for marked cards are found.

We allow Andrew to revert the change and play the Blood Moon again since this clause has been added to IPG. We also revert the change in the deck list so that it matches the deck again.[/expand]