Can You add Gecko codes?

[Spyro96]

I'm new to dolphin, I just got it last night. I figured out how to cheat already, but you can only use the codes they give you? I'm looking for a the Moonjump code (Mario Kart Wii), and it has two codes for moonjump, but neither of them work. I've tried putting codes of moonjump I found on the web, in the action replay slot (lol, i know.), and that didn't work either e_e