I believe the ammonia removing rocks are called zeolite, but I'm not quite sure on this. Someone correct me if I'm wrong.
Anyways, you'll have to put the ammonia "soaked" zeolite into a brine solution (check references for the exact concentration/salinity that you need). You'll have to put the zeolite in a filter or something and constantly keep the brine solution running through it for several hours. After this time, you can dump the now salt water (which is full of ammonia), and rinse the "recharged" zeolite with some very clean, soft water (RO or distilled water comes to mind)
Personally I don't think it's worth the hassle.
Though for knowledges sake, yes, zeolite operates on the principle of ion exchange. The zeolite usually exchanges a positive cation (depending on what kind of zeolite you have) for the NH4+ cation in the water. When the zeolite is totally "full", you can recharge it by saturating it first with a brine solution, which replaces the NH4+ cations with the Na+ cations in the zeolite. Rinsing the zeolite in distilled or RO water is important, as you want to rinse away the NH4+ cations. If you had used normal tap water, you'd be exchanging the Na+ cations for other stuff that's in the tap (such as Ca+2, Mg+2, etc.)