There's no retooling.
Originally you had Car Robot Gigatron who can only transform into 6 modes. Then they released Devil Gigatron who was retooled to transform into 10 modes. When Hasbro did Robots In Disguise, they took the Devil Gigatron mould and used it for _both_ Megatron and Galvatron. Megatron was marketed as having 6 modes and Galvatron marketed as having 10, but in reality BOTH can transform into all 10 modes because they're the same exact mould. The only retooling Hasbro did to this toy was rounded off the tips of the missiles.