Booting OS X from grub

Hi all,
Picking up from the other thread... this is about booting OS X on
apple ppc hardware when grub is being used to boot Linux.

I tried the version of the BootX file Ben Westover shared in this
message https://lists.debian.org/debian-powerpc/2023/06/msg00008.html

I placed the file in /boot/grub/System/Library/CoreServices/BootX.

I then blessed it:
umount /dev/sda2
hmount /dev/sda2
hattrib -c UNIX -t tbxi :System:Library:CoreServices:BootX
hattrib -b :System:Library:CoreServices
humount

What I expected to happen, was that on power on I would get a menu,
the same as yaboot used to have, which says something like "press l
for linux, x for mac os, c for cdrom". What actually happens is that
on power on it goes straight to grub, as it did before.

If I hold alt down at power on and select the debian option, then I do
get the "press l for linux, x for mac os, c for cdrom" menu.

However I am not really sure this is worth pursuing, because holding
down alt to select the operating system is already a working solution
for booting mac os x when grub is used as the bootloader for Linux. I
do wonder though how one would go about changing the default boot OS.

Thanks,
Ed