Have recently purchased a GDEMU, I found myself having a lot of fun finding out what we can do with this awesome and versatile upgrade replacement.
After coming across a post by Razor X on the forum Sega extreme, where he shows us how to change the menu and also how to give us access to making our own GDEMU Menu layout.
Here is a Video of how to do it yourself. Download links are below:
Original Source post by RazorX
Update (3 more themes added AtomisWave, Yu Suzuki Works, Gdemu Smart )