I don't really like that workaround because the policy system will group your app into the radio category, which has less privileges than one in the "player" category. If you want to edit xpolicy.conf, check out my headset-control package which'll add the information to whitelist headset-control (I do some libplayback stuff in it) and adds a trigger so that if xpolicy.conf is replaced by another package, headset-control's postinst will add it back in. (I happened to test that when dist-upgrading from leaked PR 1.2 to "proper" PR 1.2.)