Im a newb but you def dont want to be adding stuff to your buds when they are that close to harvest, the plants wont have time to convert what your adding to smokeable goodness.
And as far as light goes, def not more, you dont want to encourage any more photosynthesis, let them dark out and harvest just before the lights would have come on during their regular flowering cycle. Maybe drop the lights for the last 24 hours
Wait till the last 48 hours, and double flush the medium. Flush once, wait 30 min for the salts to start to dissolve, flush again. Then wait.
The medium should be dry by the time you harvest but the key for end resin production is the humidity of the room, over the last 3 days try and dry out the room as much as posible, this will cause the plants to develop more resin as protection from the dry air.