Yes, changes can stress them out. Some changes are important enough that you just have to do it, but it will take him time to adjust. A brand new tub might not only look different, but all his scents are gone, he probably feels lost and is trying to find his home. As long as he isn't being too persistent to where he is rubbing his skin raw, and his temps and humidity are good, I wouldn't be too worried about it, it will pass.

Double check all your parameters. If you are having a bad delay getting the correct size hide, I agree cutting the current one is probably your best bet, or even just cutting a hole in an empty food tub like cream cheese comes in or maybe a bit bigger depending how big your little guy is.