If you're only a week or two into flowering, you can revert it back to an 18/6 lighting schedule and return them to vegetative growth fairly quickly. I'd start adding a fertilizer with a higher Nitrogen content, and start taking cuttings as soon as new shoots begin to form.

You can reveg a harvested plant, but from what I've heard, it'll lose some potency each time the plant is harvested. Plus, reverting a mature plant back to vegetative growth, you'll either need to repot into a container that is much larger than the one it was flowered in...or...you'll need to cut away a good bit of the root mass. I always assumed this would stunt growth too much for it to be beneficial. But cloning, on the other hand, is quick and easy once you've done it a couple of times, and can produce some fantastic yields.