You misunderstood me there.
First things first - Installation & usage:
Extract the archive and copy the plugin folder to the root of your SD card. Make sure that you only use one plugin per game!
While ingame, use the [Select] button to open the menu. If it's not showing up, try pressing DPAD-Down since the menu can sometimes "glitch" the screen.
Cheats:
The Character Changer is not in this plugin, but there are tons of other cheats to choose from.
The "Unlock all FSC" cheat is equivalent to the "30 Fon Slot Chambers" cheat you mentioned. FSC = Fon Slot Chambers.