I believe you could use a NDS emulator and a memory editor. You can with the Nintendo DS Train Toolkit by datel (codejunkies.com) with you computer and the Action Replay DS, you can make codes, but it does take time and patience.
http://us.codejunkies.com/Products/NDS-Trainer-Toolkit__EF000358.aspx
There are also some applications like Pokesav (for Pokemon) for the specific game you want to make.
All of the action replay codes are long because there are so many different codes and games. As a result the creators of the action replay has to make the codes very long so your action replay can identify the code.
Use Action Replay Manager on your PC
What do you do when action replay has no free space when you have no codes?
you make them up!
With pokesav
You can make codes for your Action Replay DS by using the "Trainer's Toolkit". I posted the direct link in the "Related links" column.
Make sure you are selecting the codes you desire before you startup the game on the Action Replay DS. If you are doing that, the codes may be invalid.
What do you mean by an Action replay manager? I can make codes if that's what youre talking about.
To make action replay codes for not only LoZ: Phantom Hourglass, but for all games, go to http://us.codejunkies.com/Departments/DS-and-GBA.aspx, and buy the NDS Trainer Toolkit. You can then be able to make your own codes for a wide varaity of action replay codes! Thanks for asking!
you cannot make your own action replay codes for that game you only can make codes in Pokemon pearl or diamond with the pokesav
make sure its updated
the codes that were made by the ppl who created action replay are at codejunkies.com