Yup, that's a good question. From my research on it, I believe we have quite a while before those changes take place. Heat, radiation (like light), pressure, and dryness can speed up the process. Heat is the main one to avoid. Older bud, say at dispensaries or in your stash, will be far less useful. I'm wondering if rosin is good for this, it's just pressed resins right from the plant. You can even do it fresh, or frozen (sometimes called frosin). Tinctures too. My wife's post has a bit more info, but to be honest I think this is one area that more research is required. We know some basics, but it will be great to unlock further mysteries and get more access to the healing capabilities of cannabis.