The info comes from the files in the mod_data folder as far as I know. You can try to add a info.json there, as well as a .jpg. In-game, it will look like it is from the repo if it works.
I don't think it's possible at all, the game has ways of checking what mod is from repo and what not, so it won't work on non-repo mods
Yeah, I don't think it is possible either. Eh, it was worth a shot. (or 20, considering its been like a month) But yeah, I looked into it further and I don't think its possible. I just thought it was because I still have Shio's FBK mod and it still shows its description perfectly fine in game, but technically it was from the repo so I guess it isn't.
Could have been uploaded to repo and rejected due to copyright, but the folder could be still downloaded by the author
One of my mods was rejected and I can't download it from BeamNG's servers, so I don't think that would have been the route he took. I'll check that mod's files and see what is up with that. EDIT: So, I just checked, it appears he DID submit it to the repo as an Automation mod on July 19. There were some very detailed photos in there as well. He probably submitted it to the repo, probably well aware it would be rejected, and then downloaded the mod from the repo before Car_Killer officially rejected it. However, it is missing hashes for the files in the mod, as well as the mod's unique id, so it is possible it is custom.