Cannot append and edit AndroidManifest via config.xml for Cordova

I am trying to use config.xml to edit the AndroidManifest.xml file and I can't seem to get these two to co-exist (if I remove one or the other, then the one that wasn't removed is applied).

from config.xml:

<platform name="android">
  <edit-config file="AndroidManifest.xml" mode="merge" target="/manifest/application">
    <application android:allowBackup="false" android:fullBackupContent="false" />
  <config-file parent="/manifest/application" target="AndroidManifest.xml">
    <activity android:configChanges="orientation|keyboardHidden" android:name="com.manateeworks.ScannerActivity" android:theme="@android:style/Theme.NoTitleBar.Fullscreen">

Technically, I only really want the allowBackup and fullBackupContent attributes to be set. The activity is being added in because I'm using a plugin that adds it; but when I put the edit-config in my config.xml it clobbers the addition of that activity.

What am I doing wrong?