MDX Data Modification - Modifying Data
Applies to: 
SQL Server Analysis Services 
Azure Analysis Services
Fabric/Power BI Premium
Besides using Multidimensional Expressions (MDX) to retrieve and handle data from dimensions and cubes, you can use MDX to update or writeback dimension and cube data. These updates can be temporary, as with speculative, or "what if", analysis, or permanent, as when changes must occur based upon data analysis.
Updates to data can occur at the dimension or cube level:
Dimension writebacks
You use the ALTER CUBE Statement (MDX) statement to change a write-enabled dimension's data and the REFRESH CUBE Statement (MDX) to reflect the deletion, creation, and updating of attribute values. You can also use the ALTER CUBE statement to perform complex operations, such as deleting a whole sub-tree in a hierarchy and promoting the children of a deleted member.
Cube writebacks
You use the UPDATE CUBE statement to make updates to a write-enabled cube. The UPDATE CUBE statement lets you update a tuple with a specific value. You use the REFRESH CUBE Statement (MDX) to refresh data in a client session with updated data from the server.
For more information, see Using Cube Writebacks (MDX).