Tuning overdamper pianos is no problem at all, using a few simple
techniques.  The temperament strip is inserted below the hammer strike
line after the action is tipped back to  get access.

Tuning the unisons later is done by inserting a Papps mute between the
damper wires, also below the hammers.  You can pluck the strings with
the tip of the mute to tell where you are.  It is a little like tuning
blind, but hey, piano tuning has always been (and remains today) a
profession taken up by visually impaired folks.  You don't really need
your eyes as much as your ears.

Access to the strings is not the problem with tuning overdamper pianos;
it's usually the loose tuning pins, unless you come across a decent
example.

Jurgen Goering
Vancouver Island, Canada