I have just started using the Accelerator and frankly, I don't see why you couldn't finish your previous Accelerator while beginning a new one, as long as you list your goals clearly for each one as indicated in the Circles and keep listening sessions for each with sufficient time in between (I think a minimum of 20 min is suggested). It seems to me that the main purpose of the Accelerator is to familiarize the user with the full range of Paraliminals while using them to focus on a goal from many angles. I'm following the Accelerator for my main goal right now but I've used other Paraliminals simultaneously for more specific, momentary goals. I haven't had my Paraliminal library very long but I'm having great success with what I've used so far and I really enjoy listening to them.
Good luck with your goals!