• HLMWadExplorer[github.com] (most up-to-date version)

Open up the program and make sure your base WAD is set to the Music WAD.

If you already have a music mod ready, just click "File" and "Merge Patch..." Then, find the mod and select it. If it is a larger mod (probably due to song length) the mod will take longer to install. Afterwards, you can exit the WADExplorer and start up the game.

Assuming you knew what song you just replaced, try playing a level with the modded song or create a new level using that song as the track. If you realize the modded track was applied to an already modded track from a previous mod, use this guide to reset your music library back to the default tracks Then you can apply the new modded track without worries.