Transition for Rate Plans with Different Pricing Sources

I am currently working on a plan for a current product, has rate plans without price schemes, that has subscriptions to the same product, but with rate plans that have price schemes. The price scheme will replicated the pricing model of the original, just with some added discounting abilities included. What is the best course of action to transtition from no price scheme rate plans to price scheme-based rate plans and maintain the current subscriptions in the system?