You can do that in ..\Scripts\Aircrafts\_Common\Cockpit\ViewportHandl ing.lua
look for "render_purpose.GENERAL" (without the quotes). It's on line 57 for me.
Comment it out, and the in-sim MFDs stay dark.
So, Before
Code:
purposes = {render_purpose.GENERAL,
render_purpose.HUD_ONLY_VIEW,
render_purpose.SCREENSPACE_OUTSIDE_COCKPIT,
render_purpose.SCREENSPACE_INSIDE_COCKPIT}
And after
Code:
purposes = {--render_purpose.GENERAL,
render_purpose.HUD_ONLY_VIEW,
render_purpose.SCREENSPACE_OUTSIDE_COCKPIT,
render_purpose.SCREENSPACE_INSIDE_COCKPIT}