Can the VA reduce my rating if it shows as static?

In short, yes. A rating that has been made static simply means the VA will not order any re-examinations. If you file for an increase and a new C&P exam is done, they can propose to reduce your rating if the examiner reports an improvement. If you have had your rating for 20 years, you are protected, and they cannot reduce. If the VA does attempt to reduce your rating, there is recourse and a hearing can be requested to prevent an immediate reduction.