Re: changes in milk when drying up?
I have heard the milk can get more salty when it starts to dry up, but also can get salty when you have an infection or become pg.
As Andrea said, you can nurse out of one breast just fine and not worry about the other one. But if you're wanting to change that then you could always try pumping the other side to build up your supply.
Personally once my DS hit that age I didn't care which breast he went for, he mostly nurses on left side and occasionally on right side. At this point for us it's mostly comfort so I just let him do as he pleases with the sides.