One consequence could be that he might get in trouble with the school rules. Hogwarts is a magical place with its own set of traditions and regulations, and a Muggle device like a phone could be seen as an oddity. Teachers might confiscate it thinking it's some sort of strange magical object that could disrupt the magical environment of the school.
One consequence could be a change in the school's power structure. If Harry controls Hogwarts, the old hierarchies might be challenged. For example, the influence of some traditionalist teachers could decrease. Another consequence might be a shift in the curriculum. Harry may introduce more practical and combat - related magic lessons, given his own experiences.
One consequence could be that it alerts all the magical defenses of Hogwarts. This means that every protective spell, charm, and enchantment within the castle would be on high alert. For example, the portraits might become more vigilant, the secret passages might close off more tightly, and the ghosts could be more active in patrolling the corridors.
The Hogwarts community as a whole would be in shock. Harry is sort of a symbol of hope in the fight against the dark forces. His withdrawal could lead to a decrease in morale among the students and teachers, making them more vulnerable to threats. Also, the balance of power within the school could shift, as Harry has often been a key figure in dealing with various dangerous situations.
There could be various consequences. Firstly, a cease - and - desist order might be issued, forcing the seller to stop selling the fanfiction immediately. Secondly, the seller may have to pay damages. Since 'Harry Potter' is a very valuable brand, the damages could be substantial. And thirdly, in some cases, there could be criminal charges if the infringement is severe enough, although this is less common in cases of fanfiction sales.
There could be a power struggle within the wizarding world. Some pure - blood families who have long held influence in the Wizengamot might oppose Harry's control. This could lead to internal conflicts, maybe even a split in the wizarding community between those who support Harry and those who don't.
The pure - blood supremacists could be antagonists. They might not like the idea of Harry, a half - blood, inheriting Hogwarts and try to undermine his authority.
Obviously, Harry Potter himself. Then there would be his friends like Hermione and Ron. They could be his advisors or teachers at Hogwarts. Dumbledore might also make an appearance in the form of a memory or a portrait that gives Harry guidance. And of course, the students of Hogwarts would be important characters too.
One possible consequence could be immediate expulsion. Guns are not part of the magical world of Hogwarts, and bringing such a dangerous Muggle weapon would likely be seen as a serious violation of school rules. Another consequence might be confusion among the students and faculty. They are used to dealing with magic, not firearms. And it could also lead to a breakdown in the magical - Muggle secrecy that the wizarding world tries so hard to maintain, as guns are a very obvious Muggle item.
He might lose the support system he had at Hogwarts. His friends like Ron and Hermione would be separated from him, which could lead to changes in their relationships. They might have to find new ways to communicate and support each other.
Well, it could be used for simple things like keeping track of time. Instead of using a wizarding clock, he could just look at his phone. Also, if he has any Muggle - made apps on it that are useful, like a flashlight app, it could come in handy in the dark corridors of Hogwarts.