On the monsters are due on Maple Street if change which detail would change this from science fiction to fantasy fiction

The biggest change would be if it didn't involve aliens, but some fantasy creatures (elves, dwarfs, unicorns, dragons, etc.).

The second one would be the complete absence of the other planets and space elements, and the inclusion of other worlds, realms, and dimensions.

Finally, if the occurrences on the street, like lights turning on and off, were from the fantasy elements, and not from supernatural elements and creatures.