No one said it can't be written to bios. It's just that no one has done it. If you are willing to implement it, here are the details (you could just look this up in nkpatcher vga source code yourself):
CODE
patchvideoprogr:
push ebp
mov ebp,esp
push eax
mov eax,[ebp+16]
or eax,eax
js .cont; hdtv mode
jz .640; default mode (?)
test ah,01h
mov eax,88080801h; 720x480p
jz .chng
.640: mov eax,88070701h; 640x480p
.chng: mov [ebp+16],eax
.cont: pop eax
.frame: sub esp,1Ch
VJMP jback
Patch kernel call AvSetDisplayMode beginning to call this code. VJMP jback shoud be substituted with far jump back to AvSetDisplayMode. You should find some unused place in kernelel to put this code (there's plenty).
ok ive been trying this all wrong.
if i open it up in a hex editor, there is no AvSetDisplayMode in the code.