Your startup services lie in the /etc/rc.d folder. You will observe that ls -l /etc/rc4.d for instance, will show you these files are weighted to run in order and symlink to their corresponding startup scripts in /etc/init.d.

To disable mpd, for instance, update-rc.d can help:

sudo update-rc.d -f mpd remove

Now you will be able to add mpd to a local user script on startup without having to sudo mpd --kill or sudo killall mpd.