The A600 is permanently perpetually stuck in 32-bit mode forever and ever and ever. There is no way to switch into 64 bit mode. It can't be downgraded into 24-bit mode. It can't be downgraded into 16-bit mode. It is just STUCK at 32-bit mode period. The End.
Hmm actually this is all not true what you say.
The A600 was shipped with a 16/32 bit CPU runnign in 24bit address mode.
So be default you run 32bit code, and of couse you can also run 16bit and 8bit instructions.,
And default the CPU support 24bit address mode.
The Vampire CPU upgrade which this topic is about now replaces the CPU completely.
The Phoenix is SuperScalar and fully 32bit and of course also offers 32bit address mode.
Now enabling 64bit addresses in Phoenix takes me a *smile*.
This is would absolutely be possible to turn all your existing old AMIGAs into 64bit systems.