I did not open the gift box since few days ago, but looking at the other posts by other users, it seems that the change he tried to say is about the challenge. Previous post by coin_trader, the challenge is about to receive 50% deposit back while his challenge as shown in above SS is 20% deposit back. I'm not sure if users can get different challenge, if the challenge is the same for all users then we can say that there is indeed a change from 50% to 20%. However, if it is possible that challenge can be different between users (maybe because of the time of opening the box), then we cant say there is change.
Maybe you are right about the changes because players open the christmas giftbox at different times, those who open it early will get 50% cashback after making a wager of the amount of deposit made and those who open it late will only get 20% cashback, but the question will arise what about those who open it early but do the challenge late? which players will get 50% or 20%, so it can be a lesson when we have opened the giftbox and are interested in doing the challenge, we can immediately avoid changes because many players have completed the challenge and received prizes.