I may be wrong, but if you boot OS9, not using bye or macboot
command in OF, instead, by typing

  boot hd:,\\:tbxi
or 
  boot hd:9,\\:tbxi
etc,
  Mac OF may not overwrite the boot-device or boot-file value
at its boot time.

You may need figure out correct boot partition number which I
wrote 9 in above example.
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Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.