Bobby,
I wonder if there is a question of terminology here. Knobs vs Turrets. There are some aftermarket knobs that attach to various scopes to make adjusting easier (Stoney Point I believe). You simply screw them into the turret and they become extensions so that you don't need to use the coin slot Nikon has such an arrangement on their 6.5-20, the scope comes with two sets of oversize knobs that you attach with set-screws, one knob fits inside a cover and the other is too big to fit inside.
Changing turrets is much more technical and can only be done at the factory or at a place like Premiere I believe. The scope must be taken apart and re-filled and sealed with nitrogen.