how to re-enable services in an app (Microsoft Remote Desktop in particular)
Some (perhaps all) services are context specific. They will only be offered/enabled when they can be used.

For example, a service that is meant to act on a piece of text will only offer itself when text is selected.

You can try this yourself in Safari. Select a piece of text in Safari and check the Services menu, you should see numerous options including "Add to iTunes as a spoken track" and "Make New Sticky Note". However if you visit the Services menu in Safari when nothing is selected you will see "No Services Apply".