Well, this is fairly simple. All you need to do is while PMI'ing, just open the mission you want the songs from.
1. Go the the [lsnd] tag, the looping sound one.
2. Find any tag with the word "music" after the level.
3. Save the songs meta recursively in the New Items folder or whatever you call it.
4. When rebuilding the map, be sure to include all the song parts, and once its rebuilt, the new sounds will be in the [snd!] tag spot.
Just use HHT and go into the [lsnd] and replace any of the ambient sounds with the looping section of the soung you took, so that the song will allways play
also can be used for taking ambient noises from maps too
Like putting bird noises on a space map (lol)
Or taking something cortana said for when spartan gets hurt, lol... infinite possibilities.