Sorry, but that did not help... as for the personality tab in the opponents screen, I had already tried that. There are quite a few lines in the .raceconfigxml that are not explained in Macmatts post but neither of these, be it mentioned or unmentioned seems to help... But from that I got the idea to search through the xml files in the /Twilight of the Arnor/Data/English folder and I found the messages in the FlavorText.xml, where the text about the new age of peace is found under the tags

<Topic Name="Journal_A_Journey_Begins">
  <Dialogue>
    <Speaker Name="Altarian">2</Speaker>
    <Listener Name="Generic">10</Listener>
    <Phrase Morality="1">

And the text about doom awaiting any threat has nearly the same tags, except for

<Speaker Name="Yor">5</Speaker>

Is there a way to choose which of these a custom race uses?

Estelyen, perhaps you are not understanding what is happening here. You seem to be confused as to who is sending messages to whom.

You are an alien race that has been given hyperdrive by the Humans. That first message is from the Humans to you - an alien race. You are not communicating with them - they are communicating with you.

As a 'good' race you are threatened (by the Humans), to keep you docile and fearful; as an 'evil' race you are sucked up to, to keep you from attacking.

If you create a custom race that you want to play as a peaceful race, then lean towards a 'good' alignment (and go that way when you choose your ethical alignment) and play it that way. But you will still have to defend yourself, even so. Diplomacy can only go so far against those that will not be 'talked' into peace, so research and utilize those special 'good alignment' weapon and defense techs.

If you create yourself as an evil race - then be prepared to start aggressive, continue aggressive, and finsh aggressive.

Personally, I prefer Neutral alignment.