I think I'm a bit confused about exactly what your use case is. But it might be easiest to just create the dag with the schedule you need on a go-forward basis. Then you can manually trigger the dag for the backfills periods that you need, or create an ad hoc copy of the dag with restricted start / end and catchup true for the backfill.
Related but probably not relevant to your specific case is the events timetable, which lets you define a schedule that runs on specific pre-determined dates that are not achievable through cron. https://airflow.apache.org/docs/apache-airflow/stable/authoring-and-scheduling/timetable.html#eventstimetable
