He'd become more politically astute. As a king, Ned would have to deal with the complex web of politics in King's Landing. He couldn't just rely on his sense of honor. He'd need to learn to play the game, which would be a big change from his straightforward nature in the North.
Ned might become more cynical. Dealing with the backstabbing and power - hungry nobles in the capital would test his faith in people. He'd see the worst of humanity more often, and this could make him less trusting and more guarded, while still trying to hold onto his core values of justice and family.
He might become more cynical. In the brutal world of Game of Thrones, he'd face a lot of backstabbing and treachery. His idealism from the MCU might be tempered, and he'd become more calculating.
In a Ned Stark becomes king fanfiction, the story would deviate greatly from the original. Ned's leadership style is very different from those who came before. He would probably focus on building a more unified kingdom based on loyalty and honor. This could mean changes in how the courts are run and how justice is dispensed. His children might grow up with different expectations and opportunities. For example, Arya could be trained in a more formal way for a role in court rather than having to flee for her life.
One simple way in fanfiction could be through some kind of magic. Maybe there's a powerful red priestess who discovers Ned's body before it's fully decomposed. She uses her magic to resurrect him, much like Thoros of Myr did with Beric Dondarrion. Once back, Ned could play a major role in the political games again, this time with more knowledge and a thirst for revenge against those who wronged him and his family.
One interesting storyline could be Ned Stark ruling justly in King's Landing. He might reform the corrupt systems in place. For example, he could ensure fair trials and end the excessive use of power by the nobles. This would likely earn him both respect and enemies among the powerful families. He could also focus on strengthening the city's defenses and improving the living conditions of the smallfolk, which would be a departure from the self - serving rule of many previous kings.
Ned might become more open - minded. Renly has different views and ways of doing things compared to Ned. Listening to Renly could expose Ned to new ideas, causing him to be less rigid in his traditional beliefs.
Another fanfiction could be about Jon Snow (who is later revealed to be Ned Stark's son). In this story, he could fully embrace his Targaryen heritage much earlier. He might form an alliance with Daenerys not as an equal but as a leader, using his knowledge of the North and the loyalty of the Night's Watch to help her claim the Iron Throne in a more peaceful way.
Ned Stark as king in fanfiction would face challenges on multiple fronts. There is the issue of succession. He would need to plan for the future and ensure a smooth transition of power. His own code of honor might conflict with the cut - throat politics of the court. He would have to be more diplomatic than he is used to. Then there are the regional differences within the Seven Kingdoms. Each area has its own culture and needs, and he would have to find a way to satisfy them all. For example, the North has its own traditions that he would want to uphold while also integrating it better with the rest of the kingdom.
He might be adapted as a sort of foreign nobleman with strange powers. His Iron Man suit could be seen as a magical armor. He'd bring his sense of humor and quick - wittedness to the courtly intrigues of Westeros.
It could change it a great deal. In the original story, Robb's actions regarding the Freys led to the Red Wedding. But if he married a Frey, it would mean no Red Wedding. This would keep Robb alive and his army intact. It could also change the power dynamics in Westeros as the Stark - Frey alliance would be very strong.
He could marry a Dornish noblewoman. Dornish culture is very different from that of the North. Their views on marriage, family, and honor are distinct. If Ned married a Dornish woman, it would likely create tension with some of the more traditional Northern lords who might not understand or accept Dornish ways. However, it could also lead to a stronger alliance between the North and Dorne, which could have major implications for the political landscape of Westeros. For example, they could jointly oppose the Lannisters or other power - hungry houses.