Sadly, I think this is the nature of it. Offline Dynasty too, I'm guessing once you start one with the rosters that are current at the time, there's no going back to change it. Too much would have to change within the Dynasty. Or just my guess here.
Unfortunately, I just started a new Offline Dynasty with South Carolina, shifted conferences around big time, end of the first season. They just got some major updates (true freshmen Bennett +16, Stewart +9, and others), but I won't get to have those players at that level on my team.
Unless there's another way I'm not aware of, I'm guessing starting over is the only option.