MINECRAFT: can I turn cheats on, on a world that started with no cheats?

Say I downloaded a world of the internet and it had no cheats, can I turn cheats on somehow?

TheMaster

To turn on cheats on a already made world follow these steps:
1. Press ESC
2. Click Open to LAN
3. Click Allow Cheats so it says: On
4. Then click Start LAN World.

Guest