In the older days, all the motherboards came with a BIOS chip that held a small set of instructions to initiate the hardware interface before the operating system took over. The older BIOS was pretty much permanent unless the manufacturer released some patched. But now all the new computers are coming with newer UEFI support which is a successor of the older BIOS. UEFI has the flexibility of being easily accessed from withing the operating system itself. In fact Windows 10 has in-built support to access UEFI and make changes to it.
But if you want to customize the UEFI firmware, then you can use the open-source UEFITool software. This tool is not for the beginners and is strictly for the advanced users who have good knowledge of the UEFI structure and how all the things work. You can use it to load the firmware image file and it will show you all the various parts inside the firmware file. UEFITool can load and analyze a number of UEFI firmware file types including ROM, BIN, CAP, BIO, FD, WPH and EFI. After the firmware images are loaded, you can see all the various parts with their displayed with their names, type and subtype, description text and extra information.
If you want to edit any of these, you can right-click on them and it will show you different options. You can extract the part of memory as is, extract just the body, rebuild the firmware after modifying it, insert new modules, replace the modules and more.
UEFITool is only meant for the advanced users who have all the knowledge needed to modify the UEFI BIOS files. Because of you make any mistake and flash the faulty file to your motherboard, it can turn the motherboard into a dead brick.
You can download UEFITool from https://github.com/LongSoft/UEFITool/releases.