Action Replay DS Code Lists and Subscriptions
If you want an easy assortment of codes for various games with two clicks of the mouse rather than all the extremely difficult (sarcasm) and boring code entry, the following code lists will give you them. These includes NINTENDUDCT's subscription which has the various Mario 64 DS version 1 character modifier codes.
NINTENDUDECT's Super Mario 64 DS V1 Codes
These are NINTENDUDECT's codes for version 1 of Super Mario 64 DS. They include codes for colour changing, multiple characters, Texture changes, coin control, water everywhere, 240 stars and the amazing, extremely famous character modifiers which allow you to play as any character or object in the game, including Princess Peach and Bowser!
cheat-master30's Codes for the PAL versions of games
These are my personal codes, and ones people have converted for me. They are all for the European versions of various Nintendo DS games, and have a far lesser assortment than the other code lists. But here you have Mario 64 DS level select codes, trapped in level codes, wire frame character, infinite metal cap, vanish cap any character as well as 600 and 0cc for Mario Kart DS and infinite stars for New Super Mario Bros.
Bowser's Action Replay DS Codes
These are codes by Bowser N64 at the DS Ultimate forums. They include a huge variety of codes for version 2 of Super Mario 64 DS, including weird stuff, instant kill, star codes, Mario 64 size modifier, level warps, size and form mods and walk on water codes.
Tiger21820's Action Replay DS Codes
These codes, made by said author are also for Super Mario 64 DS, and are even more Mario appearance modifiers! And yes, they are also for version 1.1/2 of Super Mario 64 DS.
How to add the codes
Connect your Action Replay DS to the computer, and open up the Action Replay Code Manager. Then, go to subscriptions, click the add subscriptions button and paste the address of these subscriptions/code lists into the box, one at a time. You should then see them get loaded into the window, and you can now select and drag them to your main DS AR codes window. You can either replace the existing codes with the codes from this site, or drag to a custom code list, then take the codes you want and overwrite the defaults with those.
Notes
All the given codes above are free to use.
Word of Warning
Remember to only use codes for your version, otherwise there will be trouble in the form that the codes will NOT have any effect whatsoever. So read the instructions before importing the codes to make sure that they'll work on your version of the game.