What type of tools do you have to change them? I'd recommend a delrin punch, a brass punch will score the polymer. I say it's worth a try because a factory glock rear sight is only $5.99. That said, resale value of your used gen 3 will be higher with night sights... It's your call.
"There is only one kind of freedom and that's individual liberty. Our lives come from our creator and our liberty comes from our creator. It has nothing to do with government granting it."