I have a number of S sites that were originally installed via the zip file, and I’d like to switch to using github releases for updates. With the backups as usual, would it work to just empty the directory, do a git pull of the Omeka S source, and replace with the right config files and uploaded files?
And if so, I’m guess similar for modules and themes?
Yes, you can switch between a zip-based installation to a Git checkout in basically the same way as you’d upgrade or move an install, you just need your install-specific things in place (config files, the “files” folder, modules, themes).
Modules can similarly be replaced by checkouts just the same as a regular module upgrade: delete the old module and replace with the new one. A small number of modules also have Composer dependencies, and need similar handling to the core’s dependencies.