Experienced is a different version of an existing dude that’s usually of a different value and has different, usually more advanced abilities. This will be noted on their card by a bolded keyword like Experienced 1, Experienced 2, etc, with the number indicating their level of experience. As a noon action, you can replace a dude in play with another version one experience level higher or lower for no cost. So you could replace an inexperienced dude with their Experienced 1 counterpart, or swap an Experienced 2 dude for their Experienced 1 version, but you couldn’t go from inexeprienced right to Experienced 2.
Harrowed dudes are essentially undead. The main meaning of this is that when covering a single casualty, they go home booted instead of being discarded, when covering two casualties, they are discarded instead of aced, and they can be aced to cover three casualties.