It's called the basic file replacement code. You just have to use Riivolution with it, as music replacing doesn't work with Gecko.(At least, not that I know of)
I'm sorry to tell you this but Music replacing DOES work on Gecko.
I've tried it in the past and it worked just fine.
Also, Nebulon's BrawlEx pack had many music replacements when he used Gecko, before changing to the Project M Launcher due to filesize.
