Is there a way to make sure I can only open a world with a specific profile?

Solution 1:

Yes! And very easily, too. Profiles allow you to tell Minecraft where to store all its files by changing the Game Directory option in the profile. Just add something memorable onto the Game Directory (such as 1.7-snapshots) and that profile will never see your existing worlds.

How this works is, setting this to a different folder than the default .minecraft folder makes the game keep an almost entirely separate Minecraft install in the specified folder. (The only thing it doesn't keep separate is the game code itself – this is still drawn from the .minecraft/versions/ folder, which as you've found works just fine and doesn't compromise firewalling different installs.)

I use this myself to maintain multiple private modpacks separately from the main Minecraft version, and they co-exist perfectly and peacefully within the official launcher. It means that there is absolutely no danger of accidentally opening a modded world while running vanilla Minecraft (and thereby destroying the save!) or vice versa. I make it easy on myself by simply adding modpacks/[name-of-modpack] onto the end of the default Game Directory, which neatly stores all my modded Minecraft stuff in a "modpacks" folder within my .minecraft folder.