Different Texas auto insurance companies have different ways of determining rates. Credit might be a significant rating factor for one company, but only a minor factor for a different company. Some companies let you choose which driver will drive which vehicle, allowing you to match the riskier drivers in your household with the least expensive vehicles. Some don't. Some companies have discounts for owning your own home, others don't. If you aren't happy with your rates with one company, shop around and get some quotes. You'll probably get some quotes that are significantly cheaper than what you are paying now.
Insurers can adjust their rates either up or down at any time. They don't have to get state approval first, but if the state later judges that the rates were excessive, they can force the company to refund premiums to their customers. Usually, state rate changes don't affect your policy midterm, but they will affect the price of your next renewal.