First of all, here are some websites to help you with modding* http://rimworldwiki.com/wiki/Modding https://ludeon.com/forums/index.php?board=12.0
NOTICE: What is written below is not a solution, it is as close as I could get to one, and what information I could gather. If you still want to read it, enjoy :)
Of course you can, but you will need some programs and some knowledge that I don't have.
After about 30 minutes of research, this is what I know:
For editing the XML file
Go to your Rimworld game folder, and go to
mods > core > defs > songdefs
and click then on Songs_Gameplay.xml
You should be able to open it in notepad, and if not, download notepad++ or any similar program.
In this file, you have the song names and placements, when they should be played and the volume.
You can change whatever you want, but copy this file first just in case. You could of course download the game again, but holding on to the original file will save you a lot of time.
The easiest thing to do is to just copy paste the file in the same folder, and renaming it Songs_Gameplay2.xml .
For the music files
As you can see in the code, the songs come from
<clipPath>Songs/Relax
But this is nowhere to be found...
The music, textures and all are nowhere to be found in the folders actually...
That is because they are in a compressed file.
The file itself is in: (for Alpha9e) Rimworld727Win_data folder.
You should see:
resources.assets.resS
This is the file with the music in it.
I found that you had to download a program like ResEdit in order to be able to open these files, but it always crashed without being able to. Maybe someone with more knowledge about it could help...
The following will also not work
You'd think you could just go to Songs_Gameplay.xml folder, and change the music path with something on your PC, but you can't. It just got me an error ingame.
I hope someone will be able to answer, as I couldn't find anything on reddit, ludeon forums or google to do that. Maybe with more research and with another game with similarities, who knows.
Sorry I couldn't give you the answer you wanted.