Thanks to the advice of Colin Wood and Alan Briggs, I switched to a HWDIRECT
kernel. Now I can reinit adb at will! Muahahaahahahah!
Here's the dark side to this new found power. This is the message I got while
booting:
mrg: 'Quadra/Centris ROMs' ROM glue, tracing off, debug off, silent traps
mrg: I/O map kludge for ROMs that use hardware addresses directly.
adb: using II series hardware support
adb: cleanup: nothing returned
adb: ADBReInit complete
adb: adjustable keyboard at 2
adb: extended mouse <LT\^C> 0-button 3539 dpi unknown device at 3
adb: misc. device (remote control?) (2) at 7

That mouse dpi seems to be a tad bit off. Also, I have just noticed that the
third mouse button, which worked with MRG_ADB, no longer works. The mouse in
question is a Logitech TrackMan Marble. 
Here is what I got running my adb reinit program (from dmesg):
adb: using II series hardware support
adb: cleanup: nothing returned
adb: ADBReInit complete
adb: adjustable keyboard at 2
adb: extended mouse <LT> 0-button 566 dpi unknown device at 3
adb: misc. device (remote control?) (2) at 7

The dpi is different!!!
Don't ask me what the misc. device is, I have no idea. It might be confused by
the fact that I have two adb ports, but other than that I have no idea. Anyone
else with a Q650, or any model, gotten that message?
It seems as if HWDIRECT isn't the way to go, since I value being able to use all
my mouse buttons more than being able to reinit the adb system. These sources
are maybe two weeks old, by the way.
Even though the dpi reads out to an old number, the mouse seems to move at the
same speed it always did. Oh well, time to boot with my older kernel.
Xiamin