Can the main PCK file loaded by Godot be replaced while the program is running?
Yes, it can.
We can export a Mac app, and successfully replace the pck file that's contained inside the Mac application folder structure while the app is running. The next time the app starts up, it goes straight to the replacement PCK, and the old one is gone completely.
If you're delivering incremental updates to game with a large set of assets, this is good news: you can get rid of the bulky, outdated PCK file that you originally shipped, and virtuously save your user's disk space.
In case you're using this for something like incremental updates to your game, a word of caution: we don't believe that we can update ProjectSettings (aka project.godot or project.binary) while the game is running. If you need to ship changes to project.godot/project.binary, you'll either need to figure out how to update each value based on its functionality, or you'll need to require that the user restart after the update.
See:
You may NOT run this experiment in the Godot editor! PCK files don't really work the same way, there. We're interested in replacing a PCK file as it's seen when users run an exported game.
Run export.sh. It will export both a PCK file and a Mac DMG file. It will also create a file /tmp/000-test.pck on your system, which will be used if you unzip the Mac DMG and run it.
Then pick a flavor:
sh run_system_install.sh: this will use the system install of Godot- Unzip the DMG then
sh run_exported_mac_app.sh - Unzip the DMG then run the Mac app by clicking it.