That’s what this story says:
Members of the Church of Jesus Christ of Latter-day Saints will do Halloween things on Saturday, Arizona spokesman Don Evans said.
“When a holiday such as this falls on Sunday, we automatically celebrate on the previous day,” he said. “One of the Ten Commandments is to keep the Sabbath holy.”
Interesting. Is this official? I don’t remember doing this before, but maybe I’m just forgetful. (And I don’t recall hearing about that in church here — but perhaps it was mentioned when I was distracted chasing the kids.)