I do not use EDM, but I have managed to fix my problem with a quite extreme solution.
I went across the whole install of DCS and deleted anything I saw that was linked to the mirage F1. And then ran a repair. This finally did it.
I don't know what file was corrupt in the end but it was one of those.
Thanks for you patience and help @grim_reaper68!
Tu peux me trouver sur Discord sous le même nom qu'ici du jamais 😉
Chess96's post in Mirage F1BE Skins bug (missing roughmet) was marked as the answer