Are you using Tableau Desktop and Tableau Server? If you publish your dashboard to Server, whatever filters are set to when the dashboard is published become the default.
Otherwise I'm not sure if this is possible on Desktop alone.
Yes, this is one way to do it but if I have to propagate same Workbook with different filters for different sites then it is not practical. We have 50 sites for 50 different clients and we need to set this variable for each of them.
Need another solution.