I look up nose roll in various places and they all look like this that spin the tail 180 degree.
Snowboarding Tricks - Nose and Tail Rolls @ ABC-of-Snowboarding
I should have more detail for my description. The tail pivots no more than 90 degree and I don't think it needs to involve upper body rotation, maybe more of an up and down movement, similar to hop but just on the tail.
You're right of course on the nose roll. I was teasing a little based off your description.
But back to your original question, what to call the move you described? How about "nose pivot turn" or "nose butter turn". Calling it the "Not able to control my speed through turn shape turn" or "Holy hell, the tail of my board is flopping around like a beached carp turn" are a little to wordy.
If you are looking to do a freestyle move, unweighting the tail and pivoting off your nose is fun. If you are trying to negotiate a steep slope with the greatest control over your decent....it's probably not the most efficient option.