The Hunger Games: The Ballad of Songbirds and Snakes demonstrated how the Games were changed thanks to Snow's involvement, but the movie didn't cover all the alterations he made after the fact. One of the greatest shocks of the prequel was the significant difference between how the Hunger Games were conducted in the early days compared to in Katniss' story. At the start of The Ballad of Songbirds and Snakes, the brutal event was highly unpopular with Capitol audiences, and it was up to Snow and his classmates to turn them into a spectacle they would actually be excited to watch. Coryo especially was successful in this, but that wasn't the end of his contribution.

https://screenrant.com/hunger-games-snow-changes-event-after-ballad-songbirds-snakes/