Current practice here is to encourage people to use their Baptismal name for Confirmation. It is not required, but encourages them to focus on that saint.
You are free to take any saint.
My father’s name was Bennet, but the priest who baptized him was unaware of Saint Bennet; so baptized him Benedict. My father thought that was his legal name and used it throughout his life. When he died and we applied for his insurance proceeds we hit a snag. The policy was for Bennedict, but the death certificate was for Bennet. Fortunately his mother was still alive and provided an affidavit certifying that the two referred to the same person.