It is possible for more than one computer (Macintosh SE, Macintosh II, or
Apple IIGS) to share an ADB keyboard and the mouse attached to it. Switch
the data leads only, not the power switch on the keyboard.
Only one keyboard is hooked up at a time; at power-up, each is assigned the
default ADB address of 2. This default gets assigned all the time (unless the
software specifies otherwise) and so they all have the same address. Thus,
when the computer addresses the keyboard at address 2, whichever keyboard is
attached will respond.
The switching should take place when there's no activity, so as not to lose
or confuse data.
Remember: don't change the default address with software.