The RouteOnContent processor allows to define properties on the properties tab. These are then converted into relationships one can use to route the results.
When I add a property on the properties tab and then switch to the settings tab, the new property is not displayed as a relationship. But when I close the dialog (click apply) and reopen it, then the relationship is correctly shown.
This is not user friendly. I would recommend to add a third button to the processor dialog (actually to all processors), so there would be "Cancel", "Apply" and "OK". Clicking "Apply" would apply the changes - so that a new relationship or other changes would be immediately visible - but not close the dialog. Clicking "OK" would apply the changes and close the dialog.