Give it a source URL and Hangar re-downloads the file on launch, so pushing to GitHub is all it takes to update the app here. Paste a GitHub file link, a raw link, or any URL that serves the HTML. Without a source, the pasted copy stays put until you replace it.
GitHub raw links work from anywhere. For your own domain, host Hangar in the same Cloudflare Pages project as the apps and links are same-origin — otherwise add a _headers file containing /* then Access-Control-Allow-Origin: *.
Export writes one JSON file holding every app. Restoring merges it back in — same-name apps are kept as copies, nothing is overwritten.