The ROM hack does not change the graphical assets of the N64 game. The models are the same jagged, charming 3D shapes you remember. However, the atmosphere changes drastically due to the UI and text edits.
A "Kaizo" game refers to a fan-modified ROM designed to be "unfairly" difficult. This specific project reworks the entire AI logic, team compositions, and movesets of the original 1999 release. pokemon stadium kaizo rom