All Pokemon are determined at their generation when you load into a map. The characteristics determined in that generation will not reset until you leave the map again, except in cases of MOs and MMOs.
I know if you defeat/catch the outbreak where a static alpha is in a mmo you can get it to shine, but does the same apply to normal Pokemon?
This isn't a clear question, but if you are referencing the method outlined in this video for instance, then no, this method does not work for normal encounters.
But, as I think you know, Unown spawns in MMOs, and can be hunted with the method mentioned above. But as you said, it is increasingly difficult to not get dupes for this method. Unfortunately, to my knowledge, there is no necessarily better way in the entire series to hunt a specific shiny Unown. Unown cannot be bred, so Masuda Method won't work either.
I hope this helps! Please ask if you have more questions or I didn't answer your question properly