There are 2 different buildings here. It is possible to bid on a route from the other building but only the first bid on a new route is citywide. It is very difficult to switch buildings but if you have enough seniority and a bid opens up you can transfer to the other building with all seniority intact. You can't transfer to another city though and if it was allowed I think you would lose your seniority since you would be like a new hire at the other city.