I've now done that today, I'll check a pour tomorrow, but I made sure it did drop pressure and refill some headspace in both kegs (maybe I forgot to do it in both and did just one... dunno, but now both are done)

I'll see. I didn't think leaving at the charging pressure for an extended period would be a problem. I'll report back in a few days while it rests at ~10psi

I have an apple cider than when the serving pressure is at 20 psi, it doesn't foam much (pours as expected), but when I set it down to 8-12 psi, it massively foams. It was fully carbonated at 20psi (in keggerator on 20psi pressure for about 3 days, then initially lowered); I'm wondering if I'm...