Hello, this is the only Linux tutorial of how to use NDSTool.
On the entire internets, people are talking about how to do that in Windows, but not in Linux! T.T
This tutorial will change that.
Let's get started!

First, open the Terminal/Konsole.
This differs with what distro you are using.
In GNOME and Xfce it's Applications -> Accessoiries -> Terminal.
In KDE it's K-Menu -> Seach for Konsole.

Typ cd (path), like I did, /home/name/Documents/Mappiemalizering/Hackpoint/MKDSB.

NOTE: In Linux, it's important you add ".exe" after "ndstool".
Typ in the folowing code:
(path to your directory)/ndstool.exe -x (NAME).nds -9 arm9.bin -7 arm7.bin -y9 y9.bin -y7 y7.bin -d data -y overlay -t banner.bin -h header.bin

Now you'll see a data and overlay directory added and some .bins are added.
Go to data -> data -> Course.

Select a track from the Mushroom of Shell Cup, delete it.

Choose another track and rename it to the file you have deleted.

Now pick the same code you have typed in before you got the new files, but change the -x to -c and change the file name of (NAME).nds.

Start up the ROM in a DS Emulator.
Tip: If you have installed Wine, NO$GBA will work perfectly.

Choose the file you have modified, like old_mario_sfc (SNES Mario Circuit).

Yay!
It worked!

That was the first NDSTool for Linux tutorial on this world.
See you next time!