Suggestion: There should be a "Full Custom" Mode
In custom mode, summoners can only do limited things. There should be an option says, "full custom mode," when you are creating a custom game. When the "Full Custom Mode" box is checked, summoners in this game will be able to use commands to do certain things. For example, spawning minions and champions, changing stats of a unit, disabling fog or war, and more. This will be easier for some sommoners to test out things, like what will happen if I do this or that. In that case, summoners don't have to go into dominion mode to some testing. Another thing about "Full Custom Mode" is that there will be more fun. Players can create their own game modes and do all kinds of random stuff.
Now, about the client. When a summoner attempts to join a game with "Full Custom Mode," they will receive a warning says something like... "The game you are about to join is a 'Full Custom game.' Do you still wish to join?" If they have no idea what it is, they can click on the "?" beside it, and it will take them to a new window or page about "Full Custom Mode." Plus, there should be a check-box to disable this message from showing up in the future.
Of course, some summoners may try and exploit this. They may spawn 10,000
s to crash the server or something. Thus, there should be a limit to what they can do in "Full Custom Mode."
PS: English isn't my first language, sorry if you were confused by anything while reading. I hope I got my point across. Thank you for reading this.