Answering my own question… the service manual for Model Y on Tesla service website has instructions for removing and installing the the side trunk trim here:
https://service.tesla.com/docs/Mode...UID-5024587E-10B9-4014-A390-7577EC6DE526.html
It’s a pain to pull the trim out from the side of the third row seat but even more difficult to insert it back all the way on reinstall. Had to lift the third row cushion out a bit (service manual again) to give enough room to get the trim all the way down before I could get the clips aligned with the sockets on the top side. Hope this helps someone else with a 7-seater.
On the positive side, I have CCS support now….