The revamped engine in in M2TW does not allow an easy option for clone armies, as it its relies on reconstituting multiple parts of an individual model into a final product.

If you're ambitious enough, you should however theoretically be able to go through the game's files and remove the variations by replacing their entries with all of the same information. Then, the game would render every unit the same, which might give you an increase in performance.

I say "might" because the CPU will still be dedicated to making all those "combinations," even if there is only one to make, so ultimately I think that you would gain a bit of increased performance since your graphics card doesn't have to do as much work in showing you the final products - but your processor won't gain too much since it's still going through the math.