when you have created race or deathmatch via content creator .what?
this is just editing the HTTP requests from the social club website.when you have created race or deathmatch via content creator .
you can load it and make changes .
when loading it will request .json file for your race
redirect it to a local .json and then you can update your race/deathmatch with modded description and rare vehicles and more stuff ..
try it .