Light is light. Photons are photons. They behaved the same then as now. They mediate the electromagnetic interactions. By mediate, I mean they are the exchange particles which express transfers of momentum. Changes in momentum over time are forces, recall. F = dp/dt, where F is force, dp is a small change in momentum, dt is a small change in time, and dp/dt is the incremental change in momentum over an incremental change in time.
Ok, but what I wanted to know is if light still travels at c in the EW universe. I don't think it will, but not because EM is different, rather because gravity will be truly immense.