When the host player is in the process of opening to LAN, they are able to set the default gamemode and enable cheats.

Steps to Reproduce:
1: Open the Pause Menu in your Minecraft Hardcore World
2: Click the Open to LAN button (Make sure you are not already hosting your world; if you are, reload the world.)
3: You can set the LAN settings for other players just like any other survival or creative world.

Observed Results:
You will be able to set your gamemode and enable cheats when you click Open to LAN.

Expected Results:
When you click on Open to LAN, it should open the game to LAN, keep the gamemode set to survival by default if the player is alive. If a player is spectating and they had left the game & you reloaded the world, they would still be in spectator mode when they join back in.

Note: I did search for other issues like this, and I have not found any so far. If an issue like this has already been submitted, please let me know! Thanks!