Well, that gets back around to the idea of jamming an old non-ES shock in there while the ES shock is being rebuilt. Used to do that when the Penske needed rebuilding.
Usually when a shock is losing performance it is the damping getting weaker. With the old Penske you would get “clicker creep” where you had to add more and more clicks to approximate the original shock performance, but of course that doesn’t help with the high speed damping, which is set with internal orifices and shim stack, and isn’t adjustable. With an ES one could just set it higher on the dash, but I haven’t felt a need to do even that.