There are many ways to make a smooth moving cable control.  Player
Piano Company does it the cheap way, not the best.  My first choice
would be to replace the sheath with a good-quality bicycle brake cable
housing.  The best ones have a plastic liner (either Teflon or poly-
something) that eliminates the need for lubrication.

There are different diameters and you will need to get the help
of a patient and friendly bicycle shop person to fit it to the wire.
There are also special cutters that make a clean, burr-free cut.  They
should have these at a good bike shop.  Go to a bike shop where they
sell expensive bikes.  They are used to making things smooth-running.

You could also use a dry lube, such as a spray-on Teflon, but it would
be best to do it out of the piano.

Don't worry about replacing the wire after you pull it out.  The hard
part is probably the removing.  You may have to straighten it out if it
has any bends in the exposed portions.  If you have any trouble getting
it back in, it is a worthless piece of junk that should be thrown away
anyway.

Spencer Chase