I've also used for dvorak for a long time...over 15 years. I've never changed keycaps. If you're looking at your fingers while typing qwerty, learning to type dvorak on a qwerty keyboard might just be useful in that it will force you to stop looking at your keyboard and you'll find a speed up in typing just from that!

For me the learning process was very similar to learning a foreign language. At first it was hard, but once I started to get fluency in dvorak, typing in qwerty was hard for a while...but then at some point my qwerty typing ability came back and switching between the two layouts is as easy as switching computer or human languages. (when you know them fluently).

To address your fear, yes, there will a period in the learning process where your fingers get confused switching back and forth but once you get past that it goes away and switching becomes second nature.