You go for more of a mental change and now the trick or treaters that come to your door also become lesbian. You also include a few extra changes.
1st That all of them will be extra attracted to the other changed trick or treaters.
2nd The more candy they have by the end of the night the higher their sex drive will become.
3rd Their families will have no issue with them having lesbian sex no matter when, where, or how often they do it.
Thanks to your change many of the trick or treaters end up having sex with each other that night.