Past the edit window, but apparently the RAM is in slots rather than soldered to the motherboard, meaning it can be so if you take the computer apart.

So instead of the hatch on the back you need to have it done at service center (or be very confident in your $5000 Mac disassembly/reassembly skills and not mind voiding the warranty). Not clear if you can supply your own RAM for them to install or if you pay Apple prices on it. ECC RAM isn't cheap either way, but I assume buying it from Apple would be even pricier. Maybe the independent authorized repair centers will take user supplied parts.

https://twitter.com/reneritchie/status/941324098583511040?re...