I have found empirically that this can be done sporadically: 1) using xfinity mobile app, 2) go to device tab, 3) tap present device name to entire ‘about’ page which now has pencil icon to right of editable name. 4) Delete and/or edit this name and 5) save with check mark. 6) Then repeat last step above to hopefully have it save in xFi app. Name options (length / characters) seem limited and have apostrophe s added by default.
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