I was trying to avoid the manual route if possible. In my 2017 folder I have 4581 photos spread over potentially 365 days. I also want to do this for my 2011-2016 folders too
maybe not what you want to hear, but I'de move current 2011-2017 folders into an archive location via LR.
Make a copy of all files in an unknown area or spare drive outside of LR.
Import all over again from spare drive with new scheme. You'll lose all the settings in your new spot, but you have the archive if you need to revisit. I think I would go this route as soon as I printed all the stuff I wanted. I'de get rid of all the raws in the archive location unless I needed to work on something again, which is pretty rare. In that scenario, I'de simply copy the image over from the new location to the old.
I was caught in a similar scenario with my move to C1, I was missing a few years of data for some reason, so I had to re-import missing years. Lost all my changes, but wasnt really a big deal since I already printed, and already have processed jpegs. Should I need to redo something, I'll do on the fly.