How do you add user defined properties/values in to the Android manifest file?

You can add meta-data to your AndroidManifest.xml file and then read that in your application.

Write the data like so:

<meta-data android:value="bar" android:name="foo"></meta-data>

And read the data like so:

ApplicationInfo ai = context.getPackageManager().getApplicationInfo(context.getPackageName(), PackageManager.GET_META_DATA);
Object value = (Object)ai.metaData.get("foo");

See http://developer.android.com/guide/topics/manifest/meta-data-element.html