Personally I think this whole two-handed, one-handed thing is a load of *insert your favorite explative*. I hardly see any one-handed bowlers, which by definition, well a common sense definition, is someone who only uses one hand/arm to bowl. I can think of only two people that do this. A friend of mine that bowls on Fridays and Scroggins (and he's a maybe). Every other bowler uses their other hand and arm to some degree hence making them a two-handed bowler. The only difference is that the other arm stays on the ball longer. I guess they had to call it something and Kamayamaya style was taken (and for those of you that don't know what the Kamayamaya Wave is, look up Dragon Ball Z and watch Goku fire it).
Switching from one style to the other being a problem shouldn't even be brought up because the only differences are the approach and that the thumb comes out. Now if they switch sides, and say start throwing lefty when they were throwing righty, I do have some issues with that, but other wise no.
Be like water making its way through cracks. Don't be assertive, but adjust to the object, and you shall find a way around or through it. If nothing within you stays rigid, outward things will disclose themselves.