Basically all diesel locomotives are actually diesel electric, where the deisel engine is just a giant generator which feeds the electric motors. It should be extremely easy to put on pantagraphs and have it run on electric power on electrified portions of the tracks while transitioning.

Heck imagine if they just electrified the mainlines and tracks running through city centers then powered up the diesel generator for going onto branch lines and sidings

Of course the biggest benefit of overhead wires is the insane amount of acceleration it enables, plus for big climbs the locomotives don’t have to pollute so much, and dynamic brakes (where the motors are reversed into generators and the energy is dumped into giant resister banks) could be adapted into regenerative brakes to dump energy onto the grid too