A new cornea can last anywhere from a few years to over 20 years
depending on the health of the transplanted tissue (number of living
corneal endothelial cells per millimeter of the inner surface), any
episodes of graft rejection, and the underlying pathology that caused
the need for the graft (a graft done for keratoconus, a misshaped
cornea, will probably last longer than one performed because of
scarring from herpes simplex virus).  As a graft fails it becomes hazy
to white in color and the patient loses his/her clarity of vision.
--Dr. Cohn

No, If your IOP is okay, you wouldn't need another shunt just because
you're having a new cornea put on.  Your aging graft probably has
little to do with your IOP except that if your corneal thickness is
high based on pachymetry in that eye, you may be getting artificially
high IOP readings.  Remember that a thick cornea is harder to flatten
and therefore may give higher IOP readings than what is really going
on inside the eye.
--Dr. Cohn