Soon you'll be able to activate Rocket League mods with the click of a button, because Psyonix has announced the game is getting Steam Workshop support. Starting next month, modders can upload their mods to Steam using Workshop's easy-to-use interface, while tinkering-averse players can start experimenting without fiddling with files.
Some examples of mods already out in the wild include an obstacle course and a dribbling challenge, both of which Psyonix single out in their announcement post. Workshop support will be available for SteamOS and Mac as well, if you happen to play on either of those platforms.
The functionality is set to go live with Rocket League's December update, which may also include Custom Training. That was announced a couple of days ago, though no release window was indicated. You can read all about that over here.