I haven't made any rules about mods, but the idea of this campaign is to be as historically accurate as possible. So mods that focus on adding historic details or ground textures, like Lou and Robert Wiggins's airfields or Olham's rivers mod or Buckeye Bob's cloud mods would be fine. So would JJJ's realistic tracer effects mod be okay, as long as you don't introduce tracer too early (From late 1915 on RNAS Home Defence, April 1916 in general RFC use, and mid 1916 in French and German use, although I am open to correction on this). Mods that don't affect combat like the news mods or ArisFuser's historical aces mod are fine, too. I think the bombsight mods are okay, as would be Robert Wiggin's UI mod.
If your eyesight is going, we'll look the other way if you increase dot size.