Is there a rule on how frequently you should/can request a mortgage rate review?

Some banks may have restrictions eg: once every six months. However it's free to ask and you are entitled to ask as often as you like.

There's no hard and fast rule. But every 12 months would be a healthy frequency. Most lenders will have "specials" happening all the time. One lender might be 0.1% cheaper today, but not tomorrow. What we've seen with rate-hunter clients of ours is that they'll soon learn that the cost of refinancing outweighs the savings they get from this exercise. Plus.. it hurts your credit score by making >3 credit enquiries a year regardless of the products be it credit card, buy-now-pay-later, car loans, etc

Yes, there is a rule on how frequently you can request a mortgage rate review. Generally, you can request a mortgage rate review every six months, however, this can vary depending on the lender. It’s important to remember that each time you request a mortgage rate review, the lender will assess your financial situation and your credit score. If you have a good credit score and a strong financial situation, you may be able to negotiate a better rate. However, if you have a poor credit score or your financial situation has changed, you may not be able to negotiate a better rate. In this case, it may be best to wait until your credit score and financial situation improve before requesting a mortgage rate review. It’s also important to remember that lenders may charge fees for a mortgage rate review, so it’s important to weigh up the cost of the fees against the potential savings you could make by securing a better rate. If you’re considering requesting a mortgage rate review, it’s best to speak to a qualified mortgage broker who can assess your financial situation and provide advice on the best course of action.