change management for api implementation with swaggerhub codegen

I love the codegen features in SwaggerHub.  I want to build my api implementation on top of the generated boilerplate (python/flask in my case).  

But how do I handle changes?  When I change the api and codegen the server stub do I need to cut and paste my existing implementation in to the new stub, and then adjust my implemenation?

It seems like there must be some way to deal with this intelligently so I don't have to cut and paste my implementation into the new server stub every time I rev the api.

Thanks for any advice!

Mark