I've been in the community for a long time and haven't ever heard of anyone doing this. That said, the PetGo might be up your alley, it's a virtual pet getting ready for Kickstarter where people will be able to make their own pet roms.
Also, many people make custom sprites for the digimon Vital bracelet, and I wouldn't be surprised if the Tamagotchi smart also had people making custom characters for it.
Sorry, but the v3, from what I've seen, is relatively limited in how one can hack it. Also, your preview image is much bigger than the pixels where a Tamagotchi would bounce around, so it's likely the device wouldn't do things as cutely as you'd like. You'd also suffer a huge loss in resolution.
If it's meant to just be a cute time piece(since you mentioned you're not interested in pet functionality), I actually reccomend an Android smartwatch. My partner made himself a few custom watch faces with that fairly easily(according to him) using an app called Facer. Naturally, you'll want to do your own research to ensure it's something you're able to do, but it's another rabbit hole you could probably figure out with relative ease.
If you already have a V3, if you don't want it definitely don't just toss it; I reccomend reselling. If it's in really good shape odds are it'll pay for one of the other devices I reccomended.
