Wondering if the changes add to the reliability of just the tubes or if the change to 572s will extend the life of the 811H as well?
The 572 tubes won't change the load on the amplifier components at all. Same gain, same voltages, same current.
The tubes themselves are more robust against abuse. And have slightly higher inter-electrode capacitance which may make them not neutralize properly since they might be out of range of the existing neutralization circuit. This is something you can probably fix with a minor circuit mod but you'd have to know what you were doing.