Yes, go to Admin > Generic Lookups and select the Leadership Roles category where you will be able to add a new record for "Substitute Leader". This new value will appear as a choice in the Leadership Role drop down list of choices when you are working in the Leadership Roles dialog.
[Note: in the Windows app, go to Admin > System Settings > Generic Lookups. The Category is called "Roles" instead of "Leadership Roles". Each role position record also includes an 'in use' indicator. Role positions that were used in prior years but are no longer needed can't be deleted, but clearing the 'in use' box means they will not be included in selection dropdowns.]
