I believe that would be up to each timeshare's HOA. I do not believe that an individual would be able to do that on a unit week by unit week basis.
I doubt very seriously that a municipality would look at the individual resale's for individual unit weeks as a way of assessing tax valuations but would look at the property as a whole. While it probably should be/could be done, I wonder how hard it will be to fight city hall to get them to lower valuations, thus lowering their tax base. I bet it's a problem that starts to crop up in the next year or two if the real estate market doesn't rebound.