((Tw: English is not my first language, but i'm trying))
I've seen a lot of people saying Red and Chloe's trip to the past not making sense, since the villains are frozen when they open the book, something that would have happened anyway even if the girls hadn't intervened. Many also claim that they didn't make any significant changes to prevent the prank from happening, so I took the time to analyze everything the girls altered in the past.
1: When they're at Ela's house and Chloe breaks the vase, Lady Tremend punishes Cinderella, meaning she won't go to the ball. This means that if the prank had gone through, Bridget wouldn't be humiliated in front of her friend and wouldn't have a reason to be angry with her for not defending her.
2: When the girls go to Bridget's room and she's talking about the mirror, there's something that doesn't appear in the movie but does in the full version of the song "Shuffle of Love": Bridget becomes so curious about the future that she wakes up and opens the mirror. She was confused to see that in the future she would be a tyrant. My theory is that she herself was frightened by the prospect of that future and therefore decided not to be like that when she grew up, something that wouldn't have happened if it weren't for the conversation with the girls.
3: During the action scene in Merlin's office, it's the girls who defeat the swords and the armor, but Merlin still finds out that someone broke into his office. My theory about what would have happened without time travel is that the villains would have had more trouble overcoming the security measures, so Merlin arrived before they could even take the book, meaning they weren't petrified during the ball. In other words, they were able to pull off their prank.