Depends but I highly doubt it. The only way to write back would be if you had
a cube that was created through Analysis Services, then you could write back
to the cube. That still does not go all why way back to the source data
however. If your pivot table is created from data stored directly in the
sheet then there is no way to write back to the source data.
If you are talking about a Cube that was created via Analysis Services
(comes with MS SQL Server) then with an addin such as Cube Analysis and an
understanding of MDX query language, it is possible to write back to the cube.