Finally I found the missing link to set up EDID overrides on Big Sur and later, where System Integrity Protection (SIP) is enabled.
In short, MacOS also takes overrides from the path
/Library/Displays/Contents/Resources/Overrides, which is admin writable.
Based on that you can use the regular [
patch-edid.rb] workflow and put the updated profiles into that folder instead of the one on the protected System partition.
Note that for M1 Macs there is another way via the Display Manager - it’s a video; I really don’t know why it’s not a writeup.
There is an automation for the M1 version in Python though.