Its called re-vegging & its a common pratice,i learned it here on this site from another member.
After harvesting the buds be sure to leave a few small clusters of vegatation on the extreme lower portion if the plant,then chop all the rest of the branches off,now take a very sharp butcher knife & saw a circle around the root mass leaving approx 1/3 to 1/4 of the old root mass closest to the plant.
Now replant in fresh soil & give it a good shot of nitrogen rich fertilizer in its water,the plant will be in seroius shock for a week or so but it'll snap out of it & start growing strange looking leaf clusters in a few weeks,after you see the strange growth pattern the plant will start sprouting new branches & leaves that look normal,once you see normal growth the plant has been successfully re-vegged,make sure to switch light schedules to 24/7 until the plant is growing again normally,the whole process takes about 4 to 5 weeks to get the plant back on heavy vegatative growth again.