Hello!
You can rollback changes in the hosting section of your console. I'm not positive if it records the deploy history from before your migration, but I'm optimistic that it will, since I don't think this process changed much.
You can't, unfortunately, do a partial deploy or selective deploy--it's all or nothing.
☼, Kato
P.S. If it's not offensive to your culture or beliefs, I'd encourage you to introduce yourself! We are a close-knit family. It's easier to keep that culture strong when we remember that there are real people on the other end of our emails. Getting to know one another by name is a great first step.