(a) Except as provided by Subsection (b), each group shall use the uniform classification system and experience rating plan of the department.

(b) A group may file rates with the department, including any reasonable and supporting information required by the commissioner.
(c) As approved by the commissioner, a group may use rating debits or credits and optional rating plans.
(d) Rates of the group may not be excessive, inadequate, or unfairly discriminatory.