Yo can use the Eject button. The X-chip has the ability to map itself to buttons (A,B,X,Y) including the eject button. The main purpose of the eject button was to disable itself (turn the X-chip off)
However with Xbox version 1.0 there was a bug and it kept on resetting itself with X-bios version 1.0.
Then Team Evox came with version 1.1 that added LBA 48 support and a few extra features as well and they disabled the mapping to the eject button allowing the end user to select which button they would choose to disable the chip.
This way if you have a Xbox 1.0 by default the eject button is not mapped allowing you to choose what button you want to select that will disable the X-Chip and start with the MS Bios.