How to access BIOS memory?

Hello,

I have several Dell computers with a LCD display in front of. The displayed string can be changed from BIOS itself, but I want to modify it from within the OS.
I checked the CMOS memory (using port 0x70/71) but this information is not visible here (I tried to change the string and then check for changes).
I also checked the memory to see if the configuration is mapped somewhere, but I cannot find anything.

So, does someone knows where BIOS maps its additionnal memory, or how to access it if it is port-based access (like basic CMOS).

The BIOS is a Phoenix one, and is very recent.

Thanks,
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Hexa