How can I change the Game Mode of specific players? (in Minecraft 1.12) [duplicate]

Question

I'm creating a Death Race map and I want to make sure only "OP's" can stay in Game Mode 1 and all the rest of the players stay in Game Mode 2 (in Minecraft 1.12)

I tried to leave a Command Block causing specific people to stay in Game Mode 1, but it is a map with a lot of players and I want to make it possible in the future to easily change who is in Game Mode 1 and Game Mode 2.

Answer 1

Tag all who are opped:

tag player add op

Then, change game mode of opped and not opped:

gamemode creative @a[tag=op]

gamemode adventure @a[tag=!op]

Use tag command to change who is gamemode 1 or 2.

tag player remove op

tag player add op