I've recently been looking into MOGRT files in order to create editable templates.
Is there a way to do something similar but within the same AE file? So let's say I created a comp with a line of text with some kind of background graphic... and I wanted to re-use that same comp thoughout my animation, but for the text to be editable.
Is this possible?
You can use a Comp in any other Comp as often as you like as well as make duplicates of Comps.
It sounds like what you want to do is make duplicates and then use those. So, if you have a Comp with a particular aniamtion that includes a Text Layer, you can select it in the Project panel, make a duplicate, and then edit the Text Layer and use it as source in another Comp as needed.
Thanks for getting back to me... wouldn't this mean however, that I'd need to update each comp individually if I wanted to make any design changes? e.g. the colour of the text?
For text color, you could apply the Fill Effect to each TextLayer and link the Color parameter.
Then only have to the parent Fill Color. Usually you give the Layer or Comp that has the parent Fill Color a descriptive name like “Text Color Control” as well as add it to the Essential Graphics panel.
How far this goes is entirely up to you. Of course you'll hit limitations eventually as there is only so much even the smartest setup can do, but rigging up stuff with expressions and a "Controller" from a parent comp is easy enough even just with simple pickwhip expressions linked to a color expression control as in your case. Similarly, more reusability simply means being smart about using features like never changing the text color directly using the character panel in the first place but instead setting things up with text animators or even effects. Perfectly doable, you just need to work on learning and understanding these things. Once you do, a lot of stuff will fall into place organically without even thinking about it.