Good day Ed.
This may not answer your question exactly, but Tableau has released an extension that updates a parameter to the current date. The extension is called "Date Updater". The Tableau Extensions Gallery are available at:
That might work. I will have to try. The problem is in more of the refreshing of the date parameter all together. So every day I get a new upload with a new set of dates. The yesterday feature I have works as a default. But let's say I create the parameter today. So the most recent date will be 10/11/2018. Now next day my default works and picks up 10/11. Then I go for 4 more days. The default to yesterday still works. But now I need to look at 10/12/2018. I go to my parameter date and open it up but the max date is still only 10/11/2018. That is what I really need to change. I need that parameter to get the latest dates from the data source every time I open the page or refresh the workbook.