It seems not to be possible to assign a default style to a Impress/Draw table cell. This would be very helpful to ensure consistent sheet layout. It seems the Impress/Draw table implementation is only rudimentary. The real enhancement seems to be to use the writer table implementation for Draw/Impress too.
*** This bug has been marked as a duplicate of bug 90018 ***
*** This bug has been marked as a duplicate of bug 99852 ***