Just remember that your channeler has the equivalent power of a Valar (translates literally to Power or Powerful), which are the "Gods" of Middle Earth. So, even if you're playing as orcs from the 3rd age and your channeler is Sauron (which would be interesting to have a channeler who doesn't move around (stuck at Barad Dur) and whose spells are more powerful the closer they are cast to Mordor) you are still only role-playing one of the Maiar, who basically are just servants to the Valar. Sauron was just the servant of Morgoth, the great enemy of the 1st age. So in order to accurately create the kingdom of Gondor you would have to remove your channeler's powers and make them a mere king.
That being said I'm sure you can edit heraldry quite easily, if all you are interested in is your troops looking like LoTR troops, but not neccesarily having your kingdom act like them.
I hope that either the mod that is made focuses on the first age, or that there are 2 mods if enough people are interested in having a third age (LoTR times) mod.
Sorry, I'm a Tolkien geek, and a stickler for details.
