you can press control + alt + function # key to switch to a console (desktop runs on cltr+alt+f5 afaik).
If you want to disable X starting, edit /etc/ttys and find the line that starts /PCBSD/bin/pdm (that's from memory, should be along that line) and change the "on" to an "off", save and reboot (requires root priv).
Unfortunately I did try to change text mode that way. But looks like system hangs on that and nothing is allowed after, just shutdown (on laptop shutdown key). Is there at any part of the boot a way to reach X config?