Peridot Can't Fuse and Can't Get a Star Peridot can't shapeshift. That is a fact. That could mean she also can't substantially manipulate her "intended" form in any way, meaning no fusion and no regenerating with a different uniform.

Simply put, Era-2 Gems were made specifically without the ability to change their forms. No more expressions of individuality, no more possibilities of love or enhanced camaraderie, no more threat of rebellion.