Earlier, as now, to roll back from iOS 11 to iOS 10 was impossible. Apple has been sticking to its policies for years.
Some owners of iPhone 7 managed to roll back to older versions of iOS, in which there is no famous power management function. It appeared only in iOS 11.2 on the iPhone 7 and in iOS 10.2 on the iPhone 6, 6s and SE.
I also signed iOS 6 and iOS 7, but when trying to roll back to them, users had different problems.