You can’t change a Dual Position Air spring type to Solo Air without changing the CSU (Crown-Steerer-Upper assembly), and the air spring assembly. The Solo Air CSU has a small dimple in the stanchion which allows for air bypass when setting up the air chambers properly in the solo air system. The Dual Position Air CSU has no dimple- a dimple in this CSU would not allow the Dual Position spring to function properly by by-passing air when it shouldn’t. So, if changing from a Solo Air version to a Dual Position version and vice versa, you would need the Dual Position internals plus the corresponding CSU to make the swap.
See the current spare parts catalog to find all RockShox spare parts. All RockShox spare parts can be ordered through your local bicycle dealer. Please bring the part number to your local bicycle dealer, and they can special order the parts for you.