For the valve stem to rotate, I believe everything else would have to rotate too. Spring...spring retainer ?
I dont think those parts were meant to rotate at least not in a performance application anyways.
The car company's did use valve rotating devices back in the old days when there was leaded gas but when the no-lead showed up they stopped using them. Without lead in the gas there wasn't enough lubrication between the valve seat and the valve face to prevent scuffing and with the rotaters still in there it caused severe valve seat erosion.
Leave your rockers centered, I'm sure your valve guides will be happier.
Dale