The part of a domestic fare that drives the penalties for change is almost always the letter "N" in the fare basis, meaning, non refundable, and with it, specific penalties (which can vary by market and fare) for changes.

I am not aware of any case where (in the domestic tariff) the N for non refundable, does not drive some penalty for changes on any legacy network carrier in the DFR (domestic fare rule.)

There are cheap refundable fares in many markets, depending on the competition, that are just capacity controlled. The VA, QA...even some with advanced purchase requirements exist. While they maynot have penalties, and are refundable, you still cannot by a 7 day advanced purchase non penalty refundable fare, and then change it to go 1 day after purchase. Rules still apply.