This is mostly intended for 1998 Jeep Grand Cherokee 5.9 Limited owners, to mod the existing OEM stereo with an AUX input port, allowing for hooking up of Bluetooth transceivers and other audio devices that use a 3.5mm audio/headphone jack.
This does not damage or change the functionality of the stereo if done correctly. If an AUX device is plugged into the modded aux port, it "overrides" whatever audio signal is coming from the stereo. If nothing is plugged in, the stereo functions otherwise normally.