[gainsy]

""I have a 2.4ghz tx and rx - can I set up the tx to work with a second rx? (as in a second car without needing swap anything around, they would not run at the same time). Beforehand I would swap crystals but in these I cannot see how I would do it.""

You will need to make sure the receiver & tranny are the same make & their models are compatable, for example a futaba receiver wont work with say a etronix tranny, just make sure you get the same receiver as the 1 you already have
Hope that makes sense