It is no longer possible to convert an auto-numbered link to one with a label. The code is still there in MWLinkNodeInspector, but the action button is never displayed.
- Press Ctrl+K with no text selected to open link inspector.
- Paste a URL, press Enter.
- A new auto-numbered link like  is inserted.
- Select the link. The context menu lets you "Edit" it, click it.
- The "Simple link" inspector should have an "Add label" button, but doesn't.
An "Open" button should probably also appear (like in the link annotation inspector) and also doesn't.