Well, it could change a lot. For example, he might be able to prevent some of the tragic events that happened in the original. He could stop the deaths of his comrades like Jiraiya. He could also reshape the ninja world order more quickly, maybe by eliminating the root cause of the shinobi wars directly.
It's hard to say for sure. Comics have had a significant influence on the DC universe in the past, but the extent of control can vary depending on various factors like the creative direction and audience reception.
Well, he might use his reality - controlling power to make himself the most powerful ninja instantly. He could also create a world where ninjutsu has no negative side - effects. For instance, no one would go blind from overusing the Mangekyo Sharingan. Or he could make it so that everyone can understand each other's language without any communication barriers in the ninja world.
Character agency is a key element. Characters with strong agency can influence the story's reality. For example, a heroic character can change the fate of a city in a disaster - stricken world. They can make decisions that reshape the environment and the relationships within the story.
One way is by creating consistent characters. Their personalities, beliefs, and abilities can shape the story's reality. For instance, a story about a group of scientists in a post - apocalyptic world. Their scientific knowledge and moral compasses will determine how they interact with the new, harsh reality and thus control the overall story direction.
There are. One example could be a fanfic where the female Harry Potter realizes her reality - controlling ability during a particularly dangerous encounter at Hogwarts. Maybe she's facing a powerful dark wizard and suddenly discovers this power within herself to change the reality of the situation, like making the dark wizard's spells ineffective or creating a protective shield out of thin air. You might need to dig a bit to find the really well - written ones, though.
In some fanfictions, it could be due to a new jutsu he discovers. Maybe during a secret training session in an ancient scroll, he finds a forbidden technique that allows him to control people.