Where I live I mostly see this done to support the narrative that immigrants are bad, that you can't trust traditional media, and that you should be voting for the local fascist party.

Afaik the place names and date are not changed here, I suspect because that would make the perpetrators criminally liable. Instead they work by omission: take a many years old crime, don't mention the date but instead post it on facebook as if it only recently happened, in that post question why the media isn't mentioning this event or how the non-fascist politicians could let things get this much out of control, and then boost the post with help from others in the telegram group so that it reaches a wider audience.