It could be a really interesting concept. Maybe in the fanfic, Harry Potter as a character somehow enters Daniel Radcliff's real - life world. He could be confused by all the modern technology and different social norms. Or perhaps he takes over Daniel's acting career in some magical way, causing chaos on movie sets as he tries to adjust to the Muggle way of making movies about his own life.
One way could be to focus on the cultural shock. Harry coming from the wizarding world into Daniel's life would face a huge difference in culture. He could start changing the way movies are made, introducing more magical elements into the sets. For example, instead of using green screens for magic, he could actually make things fly around on set.
His friends like Ron and Hermione would surely support him. They have been through a lot together, and they believe in Harry's leadership. Also, the Weasley family in general would be behind him. They have always been on Harry's side in his battles against the dark forces.
In this fanfiction, it could be that Harry takes over the House of Potter to restore its former glory. He might have to deal with dark forces that have been lurking around the property, and he uses his skills and the help of his friends to cleanse it. Maybe he uncovers a plot against the wizarding world that was somehow connected to his family's house, and he has to prevent it from coming to fruition.
Hermione would definitely be one of his top allies. With her intelligence and knowledge of the wizarding laws, she could help Harry in making important decisions regarding Ministry policies. Ron would also be there, providing his loyalty and courage in times of trouble.
In the fanfic, Harry might take over the ministry to promote education reform. He could allocate more funds to Hogwarts and other wizarding schools. He may introduce new subjects like advanced Muggle studies to help wizards better understand the non - magical world. Also, he could create scholarship programs for students from underprivileged backgrounds.
If Harry takes over the Ministry in the fanfiction, he could use his experience to better protect the wizarding world. He has faced Voldemort, so he knows the importance of unity. He would probably encourage more cooperation between different wizarding communities. He could also use his popularity to inspire young wizards and witches to be more involved in making the wizarding world a better place, like starting volunteer programs within the Ministry.
Well, he might start by changing all the unfair rules she had imposed at Hogwarts. He could bring back the fun and freedom in the school, like allowing students to form their own clubs again.
Well, he might use his magic to solve Westeros' political problems. For example, he could use a spell to make the warring factions come to a peaceful negotiation. He might also introduce magic to the people of Westeros, which would completely change their way of life. And his skills in fighting dark forces could be useful in dealing with any threats in Westeros, like the White Walkers.