Dangerous. Don't do it!
From experience at Bayliss Machine and Welding Company (look it up), flipping belts off and on pulleys was part of working with machinery a 100 years ago but is especially a bad idea when using "V" belts. People continue to do this, thinking they are clever. Early posters have the right idea about finger shortening. A "V" belt will remove a hand just as quickly as a finger. It is a fair prediction that the one video will be responsible for a number of serious injuries, unless somehow people are warned, which is what I am hoping to accomplish here.
Interesting images from the internet are posted herewith to show where the idea came from. I hope readers will enjoy them. Modern "V" belts and grooved flat belts are nothing like flat belts from many years ago. For one thing, the old flat belts were slow and loose. But they were dangerous too.
John D