mikoscience
The steps to changing editing your FW is very easy.
The Knowledge Base guide -
How to: Modify your firmware using s1res tool from
here will guide you through, along with screenshots.
You can't really go wrong as the s1res tool will tell you if the image is imcompatible.
Also, if you use YOUR OWN firmware, you will be fine.
Make sure you read the other Knowledge Base articles which will guide you through extracting your firmware and updating your player with your edited firmware as well.
If you get stuck, you can always ask for help here as well.
Good luck.