I suppose using personae excessively will lead to warping due to constant effects?
If so, I suppose using any of the personae for less than half of any given year is ok. Is that correct?
Based on the Ringing the Changes insert in the Bjornaer section of HoH:MC, I'd likely categorize Persona as being in the same category as Shapeshifting and go with no Warping.
Agreed - based on the description on page 90 of HoH:S, I'd say the magic is only at the moment of change, not an ongoing effect, and therefore doesn't cause warping for a continuous magical effect.
Related (slightly) question: do auras affect the use of Persona?
At the moment of change, I don't see why not - it's a supernatural ability, and those are affected by auras. I wouldn't expect them to have any effect outside the moment of change.