Well I ended up doing couple of things to fake this, set some values to 0 like curvature,scanlines intensity and set an empty/transparent image for the phosphor texture mask.
Still I have to restart the room before some changes apply (like the curvature) but kind of makes the trick. If there's a better way to toggle on/off the shader please let me know.
Viewing post in Advanced CRT Shader for GameMaker comments
Hello,
Thank you for trying my asset!
Whenever you change any of the CRT object's settings at runtime, you'll need to have it call the function "update_uniforms()" to see the changes reflected in-game.
To disable the effect at runtime, If deleting the CRT object causes issues, you could also choose to disable it by setting its "shader" variable to shd_raw. This shader is more or less a passthrough shader that only handles aspect ratio and optionally curvature (which you could disable for a raw pixel art look).
I hope this helps!