Apply changes to Web App Manifest on an installed PWA
Forcing the update explicitly is not possible as per the spec. However, there's an ongoing discussion about it.
Are you completely sure your manifest.json wasn't served from the browser's cache? Or that the browser was actually served with the new HTML that referenced the renamed manifest.json?
My understanding was that you should just change the name (based on the content's hash, for instance) and let the browser do it's job. The spec says this way the browser should always request the new version. Not sure if the update should kick in immediately or before the next visit. However, I could be wrong.