It's OK, but MESS support lynx headerless roms if extension is '.lyx'. (If you rename a no-intro rom from '.lnx' to '.lyx' works fine).
You can see the code here
So I merely to tried extend that. What my patch is doing:
if image has header
load as usual
load like a softlist rom
[...]you managed to load the game(s) you are interested in, but other games will fail[...]
is not true. Header roms works as usual and headerless roms are loaded as softlist ones.Edit: For the sake of clarity I would like to mention that No-intro roms are exactly the sames as softlist ones, but with different name and extension.