"Does anyone know when and why the requirement changed?"
I'm really not trying to be a smart ass, but does it really matter? If they've changed, they've changed, and you will have to navigate through whatever new requirements exist if you want to renew your NH permit, regardless of when or why they changed.
Your best bet to see if there's a way to renew without getting a RI permit is to call the NH agency who attached the cover letter to your packet. Maybe they can tell you another way to do it. I'm skeptical that they can since they wrote what they wrote in the letter, but it seems to me that the best place to start is with the agency, or individual within the agency, that denied your renewal application.
Best I can offer.
Blues