Rollback option | Oauth code behaviour for staging

Could you please help me with these question?

1.Once the changes are promoted to production from staging is there any way we can rollback those changes?

2.At the moment we are unable to promote changes to production for a single page and instead need to promote all the changes(of all pages) in one go so is there any way here as well we can optimize it to promote the required changes only instead of promoting all at a single time.

Other question is regarding OAuth.
Is this staging feature working for changes in authentication code too? (Oauth 2.0 connect section code-configuration file)

Thanks