You can do this by editing the cube structure - however you will then be required to rebuild all the dimensions/hierarchies & define measures again. No problem if it's just a couple of clicks, however this is usually not the case. Here is my recommendation:
In OLAP Cube Studio export the full code & in base SAS modify the data source line to point to the new table.
from - Data=dataset.tablea
to - Data=dataset.tableb
To rerun this NEW code manually in base SAS, you will first need to delete the current cube in OLAP Cube Studio (or you can add a couple lines above the exported code to delete the original cube - here is my blog post on that tip:
http://sas-bi.blogspot.com/2005/08/refreshing-olap-cubes.html).
This will save you the trouble of recreating all the dim/hier & measures.
~ Angela Hall
http://sas-bi.blogspot.com