You can add one or more additional tasks to a checklist for a property or for a mission.
Add extra tasks for a property
From the property page, click on Options > Add extra checklist tasks
Once edited, click on save to apply the modifications to the next missions checklists associated to the property.
Add extra tasks for a mission
From the mission page, click on Checklist > Add extra checklist tasks
Once edited, click on save to apply te modifications to this specific mission only.