In \Addons\Config, I have a customized hud.plist; basically a copy of the default hud.plist from \Resources\Config. Among 2 other things, for the heck of it I enabled the yaw indicator by UNcommenting it out. It looked Ok while I was flying in a Cobra Mk III.
For the heck of it (not intending this to be permanent, mind you), I traded in for an Adder just to see what would happen.
What happened is that I got an Adder.

BUT the hud "reset" to the default hud, and it looked smaller / it shrinked a bit. And of course just one energy unit versus 4...
Note: I didn't bother saving my game and reloading (who knows, the modified hud.plist in \Addons might have taken over again upon loading).
Or would I had to have flushed the cache to "give" the Adder the modified hud?