For those wanting an easier way to customize your controls with this game, but didn't want to deal with editing a json file manually, I have a new mod that is available for download called the Relayer Action Mapper. You can even change your controls for your game pad with this mod.
Nexus Mods:
https://www.nexusmods.com/relayeradvanced/mods/2

Game Banana:
https://gamebanana.com/mods/505798

And here's the link to the game's PC Gaming Wiki page:
https://www.pcgamingwiki.com/wiki/Relayer_Advanced#Relayer_Action_Mapper_tool

This mod and be used with the Controller Prompts Mod:
https://www.gog.com/forum/relayer_advanced/controller_prompts_mod