Services that are disabled prior to upgrade remain disabled after the upgrade. However, the software images for the services get upgraded so that if a disabled service is enabled, it will be consistent with the rest of the XCO installation.
When you disable a service, the corresponding process also gets stopped. When you re-enable a service, the process gets started. The behavior of a microservice post-enablement is determined by what happens when the process starts. For example, when re-enabled, OpenStack polls Neutron for fresh data if that is its current behavior on start up.