Change icon theme
1. Get a copy of the desired application's folder from the system (for example the Contact app):
2. Extract the application.zip, search the path of the icons (by reading the manifest.webapp file) and replace the icon with a custom one.
3. Push the app and its folder on the data partition, exactly in /data/local/webapps using a temporary root access:
4. Get the webapps.json file:
And change the value of the contact.gaiamobile.org app
in this way
Use the JSONLint website to verify that the format is correct for any json file you want to modify.
5. Afther this change push the webapps.json file in its place and reboot the phone:
After rebooting you will se the new icon theme on your app. You can do the same in bulk, by apply the changes in the whole folder. All the changes will be restored after a factory reset or after the update.