The flair process is now automated. In order to get a subreddit flair, log into the Creative server (c.nerd.nu) through your Minecraft client and run the command
You will be sent a validation key in game, which you will then have to send to MCPublicFlairBot on Reddit. The bot will automatically set your flair to your Minecraft username within a few minutes. It will be set to a nice purple colour, so that people will know that you have verified your username in game.
For more details run
/help flair while in-game.
The existing flairs from the old system will remain untouched. If you don't care about validating and already have the correct flair, then you don't have to do anything at all. For users with the same Reddit name and Minecraft name, you can now get a subreddit flair to verify this to other people. If you have your old flair and want to upgrade to the verified flair, you can go ahead and do that too; the old flair will simply be upgraded to verified flair.