Hello Breeze49. I know this can be confusing, let me try and explain it the best way I can. Basically whatever tier you are when you enter a tournament, that is the tier you will compete in for the duration of said tournament.
If a Tour Pro enters a bracket tournament but advances to Master tier during the tournament they are still considered in the Tour Pro section.
If a Master enters a tournament and advances to Tour Master once again they will still be considered in the Master tier section of the tournament.
Hopefully this answers your question.
-WGTyphoon