As far as I've understood about transactional replication, the primary key is used by the replication mechanisms to find out which rows were changed. About patches: If you find a patch in Installed Updates in Control Panel, you can probably uninstall it from there.
The transactional replication requires a primary key constraint on each published table of a database. The merge replication doesn't need a primary key, but if there is one present, it must be replicated. Snapshot replication does not require a primary key.