How can I clear all the old variants of Tag-Filename history so I can just have the 2-3 that I use most often?
Hello and welcome!
You can use Shift+Del to remove the currently selected format string from the list.
Or choose one of the remove options from the contextual menu that appears when you click the 
button next to the format string field.
We also have a search here, which often brings up existing answers to current questions.
I have never had to use the forum before so I was not sure how to search. Thanks for the quick response.