Templates, which change the type, don't change the original BAB, saves or skill points. That is simple. But when do the features of the new type eventually apply? If you add classes (dependent on Int)? If you add new hit dice?
Suppose a 7 HD creature, on which a template is applied upon. Now advance it to 10 HD. How are the new 3 HD treated? As if the creature was advanced to 10 HD and then templated, or as if the last 3 HD are treated with the rules of the new type?
Suppose a 7 HD creature, on which a template is applied upon. Now advance it to 10 HD. How are the new 3 HD treated? As if the creature was advanced to 10 HD and then templated, or as if the last 3 HD are treated with the rules of the new type?