Open up your SD card on your computer, make a new folder in the root called SSBoggwavconv. Make a new text file and type in all of the song names you want in alphabetical order.
Pop in your SD card and run the game. If you're using the DVD5 version of the game, this step will be easy. If you're running DVD9 version, it will take a long time. The rest of this guide is realllllly long.
Glue a laptop to the top of your Wii/Wii U with a glue gun, make sure it runs Windows 98. Open up Notepad and type the original song name, two hyphens, then the name of the song you want to change it to. This will only work if you had a bean burrito for dinner 5 nights before. Digestion recognition was one of the technologies included in Windows 98 and is also compatible with the Wii user interface. After that, hop on one foot while patting your stomach for 10 minutes. If you shout ROOTYROOTYROOTY while doing it, the songs will be able to work in surround sound with a surround sound system. Make sure it's exactly 10 minutes (no more, no less) otherwise it won't work.