The mainstream psak for Yontif/Yontof/Yom Tov is that we light a second, smaller, flame rather than lower an existing one (since moving the food to a smaller flame prevents it from burning, there is no reason to lower the existing flame).
The minority psak is that lowering a flame is equal in Halacha to lighting a second one and neither one is preferrable over the other.
However, this is only when it is necessary for the food that is cooking. I have never heard that one may adjust a flame at will. And pilot light or no, turning off a flame completely is never for the benefit of the food. I myself had a pilot lit stove for years, and I’m sure many others here did too – it is only unusual nowadays, but was the norm when dinos walked.
Oomis, I strongly suspect that you may have misinterpreted what you heard. Are you positive that you received a psak allowing you to adjust a flame up and down at will?