I want to open the Install Connectors dialog from the command line instead via Eclipse | Preferences | Team | SVN (the button to open this wizard is usually missing from the Preferences UI due to some bug in the Subversive plug-in).
So how do I ...
Here is a screenshot of the wizard that I want to open:
I suspect the button is intentionally shown only if no connector is installed yet. Therefore, uninstalling the existing connector (in Help > About Eclipse IDE click the Installation Details button, in the installation details dialog in the Installed Software tab select the connector and click Uninstall...) should display the button again. If you think another behavior would be better here, you can report it to Eclipse Subversive.
Alternatively, an SVN connector or other plug-ins can be install headless directly from the command line using the p2 director.
Scripting the UI, e. g. open a dialog on startup, can be done with Eclipse EASE. Use the Eclipse PDE's Plug-in Spy to get the ID of a wizard.