Hate the default F-86 livery (green camo)

[greyseal494]

Is there a way to change it when running instant action missions?

[dmatsch]

no.  the instant action missions are part of the core DCS.  You can, however open them in the mission editor, make your changes and save them to a different file location.

**if you re-save the core mission, it will break integrity checks and will get overwritten 

[Lace]

You could just swap the names of the liveries, rather than edit the missions.  Maybe that would pass the IC?