I am reporting back of my experience.
Today my Spire expires on 31st December 2019 according to the app. I renewed my Ambassador membership, few minutes later I checked the app again and the Spire expiration date is changed to 31st December 2020.
I have qualified for Spire every year since they introduced the level and have renewed my Ambassador every year. So the extend Spire for one more year by renewing Ambassador works for me so far.