I recently received my HA Yellow. I elected to follow the emmc install route, and cannot find a (supported) way to edit /boot/config.txt. As a result, I cannot enable my RaZberry 7, which fits nicely inside the official Yellow case.
There is a workaround, but it requires installing an add-on that (by design) breaks the security model of docker.
Add toggle buttons for common config.txt entries in the Settings - System - Hardware menu when a CM4 (or perhaps other hardware with emmc) is detected. These should probably have the Advanced mode flag so they aren’t enabled by accident.