Unless it's a sativa further growth in flowering averages more like doubling it's height but anyway yes you could switch it back to vegetative growth but that adds a huge delay like 3 weeks at least, then another 2 weeks to go back into flowering. All said and done you could have started and finished a new crop in that time so it's best not to do it.
Also what kind of light? I'm betting you don't have a light strong enough to support the height you'll have already if you haven't trained it to stay short or won't be tieing it down.
If you want to double your harvest just bend her over and tie her down and drop the light closer, then rather than one fat bud on top you'll have fat bud all over the whole thing.