If memory serves me right then in Yosemite it was possible to set the NVRAM variable
nvram boot-args even in normal full boot mode.
This seems to have changed in later versions of the OS.
In Sierra this results in an error message:
sudo nvram boot-args="-v agc=0"
nvram: Error setting variable - 'boot-args': (iokit/common) general error
If I issue this command in recovery mode it is still accepted without error in 10.12.6.
In SingleUser is it is likewise rejected.
Was this changed from 10.10 to 10.12? Why? Why doesn't it work anymore in normal boot mode but still in recovery?
Any insight on the above is appreciated. But the single question I like to have an answer to is: how can I set this NVRAM variable in either normal boot mode or at least in SingleUser boot mode?