Oh you poor guy, you have left "real" jeep land long, long behind. This is just a glorified fiat 500. I mean, its a nice car and we like it a lot but it is not a jeep like you are used to. You are getting set up for some tremendous disappointment.
None of the compasses have a low range, it is just a marketing farce, so no its not something you can add. The trailhawks just have a slightly lower ring and pinion ratio in the diffs and are programmed to start in 2nd gear until you press the "low" button and then it just goes into first gear. This fake "low range" is nothing compared to a normal low range in a vehicle with a transfer case. There is no transfer case in any model. While we're at it, there are no lockers available for the differentials either.
The trailhawks use their first gear gimmick to net a 20:1 crawl ratio. Yours should already be roughly 17:1 in 1st gear (not 100% positive about the manuals, my first gear in our 9 speed non-trailhawk is 17:1). This is peanuts compared to 60:1 or more in wranglers and trucks, and obviously you have little to nothing to gain by going through a huge headache and expense to go from 17:1 to 20:1.
These are straight-up not real off-roaders like you have played with in the past, they are highly capable cars. They are too-far departed from real off-road machines to bridge that gap either, adding lift and big tires and such is only going to maroon you in a sad land where you have totally ruined the nice on-road characteristics of the car and you are still going to get laughed out of the off-road park by guys in wranglers, and even dudes in 2-wheel-drive toyota tacos. You can give the subaru guys a run for their money but thats about it.
Its a harsh reality but not bad if you accept it. We drove ours up a mountain road last night and still had fun but no sense in pretending this is any relation to a wrangler.