Onslaught, changed my mind, want to join Empire not Republic, restart possible?

hey everyone,

i know this is a long shot but whatever, i just began Onslaugt and I joined the Republic but (like an idiot) I realized after a few minutes that I'd like to join the Empire after all, I'm already on Ossus but haven't done anything on Ossus yet, I can only reset the mission so far because I'm already on Ossus.. but I want to go back 2 missions, all the way to the ''Talk to Lana'' moment where she asks you wich faction the Alliance shall support. I can't abandon the mission either (probably because it's a class/expansion mission), does anybody please have a way for me to restart this mess, a.k.a go back far enough (''restart'' 2 not just one quest) so I can pick the Empire and not the Republic.