If I want to remove packageX-3.0.0.deb from a published repository, what are the steps required to do so?
you would need to drop package from whatever is being published (snapshot/repo), if that's it snapshot you need to modify snapshot source and create new snapshot, after that depending on snapshot/repo you can do
aptly publish switch or
aptly publish update
distributionsunder common prefix, the only limitation is that there should be no conflicting packages between distributions, as they all would share common package pool
Stable releases are signed by both the ftp-master automatic archive signing key in use at the time of the release, and a per-release stable key.