I've seen it implemented where a price change is actually a new, separate subscription plan. So, each plan has an id, and you disallow any new signups for cert

I've seen it implemented where a price change is actually a new, separate subscription plan. So, each plan has an id, and you disallow any new signups for certain plan IDs but still allow them to be active for billing purposes( for older clients). Only show and allow signups for the new plan IDs.