Instructions
Turn off the Nintendo DS. Plug "Pokemon Pearl" into the game cartridge slot of the Action Replay device. Secure the Action Replay device by inserting it into the normal game slot of the Nintendo DS.
Turn on the Nintendo DS. A game icon might appear; simply tap it to run Action Replay. Wait for the Action Replay to load and select "cheats" by either pressing the "A" button or double-tapping the word with your Nintendo DS stylus.
Find your game title under the subheadings and select it. Choose "Add New Code" from the menu and manually enter the title of your code. For this specific cheat, title it "Swap Pokemon Players" or something similar.
Enter the code exactly as written, where each line of code is an entire line.
To swap gender to a boy, enter:
94000130 FCFF0000
B2108818 00000000
20000290 00000000
D2000000 00000000
To swap gender to a girl, enter:
94000130 FCFF0000
B21C4D28 00000000
B0000004 00000000
200002E8 00000001
D2000000 00000000
Double tap to select or press enter. This saves the code you just entered. Back on the cheat feature, manually find and select your newly input code to activate it. You can do this by clicking and dragging the code onto your Action Replay list. After that, just start up the game normally and look at your swapped character.