What do you mean by "stopped registering the .rpm file"? Please create an issue on GitHub about that.

Also, you can already copy and paste the webapps on to a different device. Just copy the config file and the profiles directory in the user data directory (https://pwasforfirefox.filips.si/resources/installation-directories/#user-data) to another device and run "Update web apps" from the extension settings on the target device.