can i cut off the top big buds at harsest time and then turn lights back on 24/24, re-vegg, switch back to 12/12 and have another harvest?? Pic's below are of my newest grow, 40 days from seedling, 7 days flowering.
Technically you can, but the plants would most likely be root bound and the soil pretty much exhausted of nutrients.
Probably better to harvest the tops, go 24/0 to force re-vegging, then take clones and use clones for next crop ... they will be more vigorous and produce much better buds than making the old bird go through it all again.
I don't think you'll get anything from a used plant...especially because it's ready to die after harvest. Like Grumpy said though, clones are a good idea if you can do that.