I haven't worked with UEFI in quite a long time. When you say 'replace the firmware', what do yo mean by that? The entire firmware including the reset vector and all code to initialize the hardware (memory training, etc)? I didn't know UEFI is allowing an end user (as long at the code is signed) to completely replace the system's firmware. I also wasn't aware that vendors were open sourcing their reference code in an open source fashion so an end user could build their own firmware.