I've seen many people asking for the ability to create custom championships for AMS, and it is in the roadmap to be included at some point, but in the meantime, here is a quick and simple way to do your own.

go to your AMS install folder and then open 'Series', you should see a bunch of srs files

Now you need to do a bit of digging and open each one until you find the car you're looking for (they're in the order they appear in the AMS ingame home page), in this case I'm modifying MetalMoro chamipionship:


Scroll down to the section called 'SceneOrder'. Now comment out (or delete) the tracks you don't want by using '//' in front of them and add some reiza/mod tracks below.

Get the track name by going into gamedata/locations then into the track you want and look for the variant

eg: gamedata\locations\road_americaCART\Road_America_SU, you use 'Road_America_SU as the track name.

And that's it, quick and simple!