Sounds like it would be more trouble than it's worth. You would have to
unsolder the bandswitch and replace it with one with an extra switch
position. Then you'd have to add a 160 meter tank coil. The only thing
that would likely fit would be a high-power powdered-iron toroid. The
tuning capacitors would likely not have enough range -- you would have
to add switchable fixed capacitance in parallel with both of them.
It would probably be easier to build a separate 160 meter tuner and
use the MN2000 to switch it in as appropriate!