hum, what do you mean by "change the program type" ? Well, to use A/B test, you need to use Email Program...
The flow you are already configured to send out email should be a smart campaign, not by using control Parnel, so that the control panel will be still avaible to make a A/B test. And you can make a smart list to say if emails are already in my smart campaign send email flow, then they won't be inside my A/B testing. is that what you are look for ?