Approach for schema changes minimize downtime

We have built a data mart consisting of 50+ fact and dimension tables running Oracle Exadata 11.2.  Microstrategy analytics use these structures.  We routinely need to make modifications to these structures, including adding columns, removing columns, changing ETL logic which will result in a complete reload of a fact table.  When we put a new release into production, it requires downtime for the Microstrategy business users.  We are looking for approaches to minimize this downtime.