Some of the different brand knuckle style couplers will work together, however a knuckle coupler will not hook to a rapido coupler. Most people end up using all knuckle couplers since they look more realistic and tend to work better. If you want to mix, you'd have to create a car with a knuckle coupler at one end and a rapido coupler at the other end to transition between them.
Usually it is not difficult to change the couplers out, but that is unique to each specific model. I'm not familiar with Bachmann N scale.