I've been wiggling through this topic, and there are some fantastic modifications on here! The one I like the most is the glow in the dark mod, so I just bought some of this:
http://tinyurl.com/cr3l7su <-- eBay link, shortened with tinyurl as it was huuuge!
A sheet of glow in the dark, photo printer paper! Some people mentioned that they wish they hadn't used plain printer paper for custom backgrounds, so I figured it would be better to get his. Best of all, it can be printed on, so I could so some glow in the dark designs!
I figured one A4 sheet was enough to do several Tamas if it works out! I'll certainly post photos of how my experiments work out, I have a very beatup v1 that I'll use as a guineapig for now!
I have one quick question to ask, and if anyone knows, that would be fabulous! Does anyone know the exact dimensions of the backing paper in mm found in the Tamagotchi? It would be super helpful for my planning if anyone does know :>