PS message vs unsubscribe link

I’m about ready to start sending my first cold emails, only a few hundred at this point, but obviously going to scale that number up. I’ve read a few posts about people putting in a “p.s. if you don’t want to hear from me again please reply “stop.” Or something like that instead of an unsubscribe link. Is this Soto should be doing? Is it in violation of any rules? Can I get in trouble? Thanks