spoiler
So, if I decide to go and beat Ganon early to unlock the completion tracker, the game resets back before the fight after credits roll. So does that mean I can do the the rest of the main story also (phenomena and so on), or do I get locked out?
Nothing becomes unobtaineable or unsolvable by completing the game once. Even the boss itself can be refought an infinite amount of times, so don’t worry about it ;)