I was going to suggest setting the %s as default in your preferences but I couldn't find any preferences for the Mosaic plot (only if you want the plot or not). The broadcast will work (at least for the main part of the charts) if you have multiple charts open. Also, if you set one chart up and use the column switcher the %s will stay.
Everyone else, please like Ron's post if you want the ability to get rid of the decimal point on %s on the Mosaic plot! I would vote for the option for the % sign as well.