The letter in Owzer's House is stored in the SRAM, not the ROM, so there's no fix for it if you have already reached that point in the story. The softlocks that were fixed should stay fixed as long as you don't load a savestate on that map. For example, if you made a save state at the top of the Fanatics Tower, that savestate already has the bug loaded. You would need to load a save state either in the Gem Box room or on the staircase maps.
So that means that there is no way for me to get into the opera house in WOR to fight the dragon or anything else there?