The only way to switch an existing world to Hardcore mode is to use a third-party app to edit the game's files. How to change game modes in 'Minecraft: Java Edition' 1.

Changing gamemodes in Minecraft might be considered cheating in some cases, but it can allow players to do a variety of things mid-game.

In Java Edition, users can also change the game mode to Spectator. That feature is eventually coming to Bedrock, too, but for now, most crafters will lean towards either Creative or Survival mode.

From building new worlds to installing mods, you can do pretty much anything. When you start a "Minecraft" game, you have to pick one of several game modes to play in - Survival, Creative, Adventure, ...