I believe it is possible, but I’ve seen a lot of guys use Bondo to repair any damage, then prime overtop.
Quick Safety Disclaimer!
I have no idea if Bondo or any paints will effect the integrity of any helmet, if the manufacturer can’t tell you then it’s the risk will all take painting a helmet.
In that case have at it! You would be able to use high build primer, it just depends how deep the marks are. Bondo will do the job whatever, you just have all the sanding to get into. But that’s all part of the fun and would be the same with straight primer anyhow. If I can find a couple good videos I’ll post the links here, but it’ll probably be tomorrow as I’m beat .
I’m finding it tough to locate the video where Bondo was used, but I have found one from Simon Murray who is involved with Createx. It’s more about preparing a new helmet, but there might be some useful info in there.
I have done many,many used helmets that have had chips ,dents and scratches. You may be able to sand tiny scratches out, but other marks i use body filler . Sand back smooth and then use automotive primer. Works for me.