I prefer
WinHex, though any decent hex editor would work. Most modern mobos use integrated flash firmware, though some models might use multiple chips or even sockets. The mobo manufacturer's BIOS flash software is usually the best choice and avoids direct contact with the hardware. You can always get generic flash software from Pheonix/Award or AMI, though it might not always work with any given board.
Modifying your firmware at the byte level is not trivial. It contains critical BIOS code and data which provide the logical interface for the entire mobo chipset. It contains the BIOS setup program and likely also contains megabytes of other software used for detection, diagnostics, and recovery.
You're unlikely to improve or add functionality unless you reverse engineer the entire mobo chipset and disassemble all the existing firmware code. In fact, you're far more likely to kill or cripple your mobo.
The safest changes you can realistically expect to do would involve changing text strings and graphic images. Many OEMs are paranoid bastards and employ checksums or other anti-tampering logic to prevent stuff like their copyright messages and part serial numbers from being altered. What this means is that changing even a single innocuous byte could prevent the BIOS from loading, thus prevent the mobo from working.
Some OEMs provide software which will allow you to flash your own custom pre-boot images or text into the BIOS. This might be good enough for your purpose.
SMBIOS editing/spoofing software is also available, a perhaps better alternative to actual BIOS flashing, though it can be tricky to use correctly.
Whatever you do, I recommend
- you disable all BIOS-level passwords before doing anything
- you backup your existing BIOS before continuing, then as always, actually confirm you can recover data from the backup before you move onward; you may need to reconfigure hardware jumpers or have a floppy drive (and disk)
- you make sure you're using the correct software for your particular BIOS and you follow the instructions carefully