Question: What was the point of changing "Twin Pines Mall" into "Lone Pine Mall"? This change doesn't affect the series' plot at all, so what was the reason behind it?
Answer: It's a small but noticeable change in the timeline as a result of Marty's time travel. The first we see when he returns to 1985, confirming that his actions have altered the present. It was originally called "Twin Pines Mall" because there were originally two pine trees; Doc reminisces about "Old Man Peabody" trying to breed pine trees on the land where the mall stood. When Marty travels back to the same place in 1955, it's Peabody's farm, and making his escape, he runs over one of the two pines (and we see the mailbox with the name "Peabody" on it). Therefore, when he returns to 1985 having destroyed one pine, the mall is now "Lone Pine Mall", because in the new, altered present, there was only one pine tree, not two.
Answer: Just to show how actions in the past have had a knock on effect on the future, giving audiences a heads up that things have been changed. Alternatively just a fun thing for audiences to notice.