The DNA of a plant, as the DNA of a human being can be altered by a constant contact of chemicals, or radiations. The feminized seeds are made by 2 ways (i know and IM SURE IT WORKS) taking seeds threw a chemical prosses, or putting them under a radiation prosses, thast why they are much more expensive than regular seeds.

You cant change the sex of a plant just with magic, what youll create is a mutation of the plant, and maybe make it develope the other gender flowers, BUT ONLY WITH A CHEMICAL PROCESS, OR RADIATION....

Dont fool yourself with idiotic sayings, its like if a girl would grow a penis if at night she gets her feet at 45°C every night for a couple years... THIS IS JUST ABSURD!!!

if you think the light or something so absurd as this will make a mutation on your plant, justr try it, over and over again, youll see how stupid your ideas are