change the pokemon trainer's name to ash. I always accidentaly call the pokemon trainer "Ash Ketchum".
You can call him whatever you want. Official names are only for uniformity purposes. You could call him Tim Tebow if you wanted to.
You're not really playing as Ash anyway, you're playing as the Pokemon he has in his arsenal. The name "Pokemon Trainer" implies that, as opposed to "Ash" which would imply that you were playing as him.