I'm not quite sure about the switch but the reason for Geordi bein the conn officer was to have a blind man flying a ship and all the symbolism associated with that. As far as the switch I think it was mainly to let Geordi's character have more screen time.
Yeah, I'm sure we've all heard this before.
Anyway, I'm glad they made the change -making Wes the helmsman. It was an idea based on a rather lame joke considering, really, Geordi wasn't blind.