Hi,
you can change the startup behavour with the eject button. Look for a small file on the root of your E partition (I believe it is called boot.bin). If you delete that file, it will boot the M$dash when you power the xbox with the eject button. If you want to boot something else, you will need to adapt the nkpatcher and recompile it.
You can backup the eeprom with the evox dashboard backup feature. You should find it afterwards in the e:\backup folder. The kingroach Ndure package can install evox on the e partition for that purpose.
It's always good to have a copy of a standard M$dash. (C and E partition). You can extract them from a Slayers Rescue disk package. The eeprom.bin is the key to unlock your harddisk. That's the most important thing to have backupped. It allows you to create a new harddisk from scratch, without hotswapping.
regards.