Dominion Yes, it would be a great option if it's right within comment box. So, when Administrator going to reply, he/she can select predefined reply right from there. They don't need to go elsewhere.
And one more thing, there should be an option to search "Predefined Replies" such that they even don't need to spend time to figure out which reply then need to send.
It would be great if you can enable preview of those "Predefined Replies" along with it's title. So, Administrator can easily see what's exactly they are going to reply.
Hope this helps.
:Malay