One possibility is that Merlin's revelation of his magic could lead to a change in his relationships. For example, his friends who were previously unaware might react with shock, some with fear and some with acceptance. His enemies, on the other hand, would likely see him as an even greater threat and might plot more vigorously against him.
She might be shocked at first. Given that in the original story Morgana has her own complex relationship with magic, seeing Merlin's magic could stir a mix of emotions in her, like envy or a sense of relief that she's not alone in her magical abilities.
Uther might initially be shocked. He has always been so against magic, so he could be furious at first. He might feel betrayed by Merlin, whom he has known for a while.
The storyline might progress with a lot of drama. People's reactions would be the key factor. If he reveals it to Arthur, for instance, Arthur's response could either make their friendship stronger or break it apart. This would then lead to different paths for Merlin, either having to hide again or standing up against all odds.
Well, Arthur could feel betrayed at first. He has been brought up to believe that magic is bad, and here his closest friend has been hiding this big secret. However, as he realizes how Merlin has saved his life and the kingdom many times with his magic, he might come to accept it and even see the potential of magic being used for the good of Camelot. For example, Merlin's magic has defeated many enemies secretly, which Arthur might now understand as a necessary protection for the kingdom.
The father's reaction varies. In a particular fanfiction I read, the father was first in disbelief. He couldn't believe that the young man in front of him was his son Merlin. Then, as Merlin showed some signs or told some stories that only his son would know, the father became overjoyed. He started to tell Merlin about their family history that Merlin didn't know before, which was a very emotional and bonding moment between them.
Merlin could choose a moment of deep trust between them. After they have shared some important experiences, like winning a difficult battle together. He might feel that Arthur is more open - minded at that time and would be more likely to understand his use of magic. Also, it could be that Merlin is tired of hiding such a big part of himself from his best friend and decides to take the risk of revealing it.
Well, it might lead to him being ostracized in some communities. Since he can't hide his magic, in a society where magic is feared or not fully accepted, people could shun him. This would make it difficult for him to have a normal life among non - magic folk. Also, it could potentially expose Arthur, his friend, to unnecessary risks as his association with Merlin becomes more obvious.
Well, Merlin's magic could change the Game of Thrones story in many ways. His powerful magic could potentially stop some of the major battles. For example, he could use his magic to create illusions and mislead the armies, making them retreat without a real fight. He might also be able to heal some of the key characters who die in the original story, like Ned Stark. This would completely change the power dynamics in King's Landing and among the different houses.