Altering Doom music

I recently downloaded a cover of the Doom soundtrack. I thought it would be pretty cool to replace my current Doom songs with the covered versions. How would I do this?

Sort of depends on the port you're using, but assuming you're using ZDoom all you should have to do is make a new PWAD with the wad editor of your choice and simply import the MP3 into it and give it the same lump name as whatever of the original song(s) you are replacing. For example if you're replacing the MAP01 track, you'd import your mp3 and name it D_RUNNIN.

See the articles on the Doom wiki for a full list of song names for each map slot.

PrBoom-plus will play MP3 and OGG tracks directly if they're dropped in the port's directory and renamed to match the music playlist at the end of prboom-plus.cfg (or edit the config file to match the tracks). Same should apply with glBoom-plus.