It looks like the best way to save/set/restore keyboard buffering (and
anything else that is editable throught the control panel) is to use
GETBPARAM to save current values, to use SETBPARAM to update the battery
RAM buffer with appropriate values, and then to call $E1/0094 to set the
system into the state indicated by the battery RAM buffer.
Restoration is similar: use SETBPARAM to update the battery RAM buffer
with the saved values, and call $E1/0094 to set the system to its original
state.

This works well, and uses only documented tool calls and entry points.
[Note that $E1/0094 needs to be called in 8 bit native mode - which the
firmware reference does not tell you].

    Bit  Value  Description
    ---  -----  -------------------------------
     6    $40    Shift+CapsLock=Lowercase mode
     4    $10    Keyboard buffering
     3    $08    Dual-speed keys
     2    $04    Fast space/delete keys


For example, to turn off keyboard buffering without altering the user's
Battery RAM, you can do the following:

             pea 1                   ;number of data bytes
             pushlong #modesToClear  ;pointer to data byte
             pea 5                   ;modeCmd = clearModes
             _SendInfo
             ...

modesToClear dc.b $10                ;bit 4 = keyboard buffering


Note that the user's control panel setting will become current again if they
hit Command-Ctrl-Esc (the system calls the TOBRAMSETUP vector at $E10094 to
update the system from Battery RAM).