1. Open notepad
2. Write: C:\Progra~2\ManiaPlanet\ManiaPlanet.exe /useexedir /singleinst /file=%1
2.1 Make sure you wrote the correct path to your ManiaPlanet.exe (Progra~2 is the same as \Program Files (x86)\ in my case), note that you can't use blank spaces in the file path and thus write \Progra~2\ instead.
3. File -> Save as: save it anywhere
3.1 Save your file as: yourfilename.cmd
4. Right click on any saved track: Open With -> Choose Default Program
4.1 Browse to where you saved the file and select the file you created (yourfilename.cmd)
5. Done!