Guy wires attached typical lattice towers are unlikely to work well. In order for a guy wire to pick up much load, the attachment point has to deflect a significant distance. The deflection in an unguyed lattice tower under full design load is going to be less than a few inches. The deflection in an unguyed wood or steel pole under full design load could easily be a couple of feet. The tension in a guy wire attached to a lattice tower will probably depend more on ambient temperature than on the structural loading of the tower. (Note that guyed lattice towers do exist, but they are a completely different design. They have a pivot point at the bottom to allow the entire tower to deflect or rotate under load).
If the tower under consideration experiences a failure, I don't see how the insulator attachment type will protect the substation equipment. If you are referring to failures further down the transmission line cascading towards you substation, reframing it as a deadend won't help unless you specifically design it as a weak link. Only if the tower were actually a full tension deadend could it measurable improve reliability. However, since this seems to be a tangent tower, reframing as a deadend would not add reliability. I think the deadend hardware and splices would actually result in a marginally less reliable configuration.