unpack / pack .apk

i want to make simple browser app that displays html files from /assets in a full screen WebView.
The idea is , Any user can change those scripts himself without need of recompiling the APK.

i try simply to :
Rename .apk to .zip
Extract .zip
Zip the folder to .zip
Rename to .apk

once my phone tries to install the new APK, a problem arises related to parsing
any recommendation to make above procedure correctly

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