You're over thinking this... None of these are specific to this type of deployment. If you want to do any of the above, you'll have to work around whatever production deployment solution you have.

1) How would you do this for any deployment method? You'd have to be able to ID one specific node in the cluster or make sure that your job could only run on one node with some sort of locking.

2) If you're deploying multiple versions of an application in production, you have other issues.

3) How would you rollback database changes to begin with? Come to think of it, how are you going to deal with any DB schema changes? This isn't just an issue with .deb/.rpm deployments of code - you'll have to figure this out for any application deployment.