If you must re-hydrate, this is the most mellow and least-damaging way of doing that I have tried:

Place over-dried buds in a brown paper bag. Place this bag inside two turkey bags or contractor bags. Place a flour tortilla, or part of one, between the brown paper bag and the plastic bags. Carefully not to use too much tortilla. Close the two plastic bags and allow to sit for 12-36 hours, checking every 12 hours. The moisture from the tortilla will slowly and gradually be absorbed by the bud. The brown paper bag prevents the bud from coming into contact with the tortilla and plastic directly, and helps even out the moisture that is being absorbed by the buds. Sealing it air tight in the plastic bags further helps even out the moisture. After the buds feel right, remove the tortillas and allow the bud to air for a little bit. Reseal it in the plastic bags and check on it again in a day or two. If done right, the bud should no longer be over-dried, the moisture content should have evened out, and much of the aroma and flavor will have returned.