The first change was to reduce the need to track hits down from 12 to 6 hits before being eliminated. Driven by a practical need not to have two dice sitting behind a unit and have one instead, much neater with just one. This also meant halving the number of hits by using a D3 approach and rounding down so the results are 0,1,1,2,2,3 a bit average dice like and providing more consistent results.
The second change was to the volley which doubles the hits rolled. A very powerful attack for regular infantry. Muskets have a range of two squares (12" if you like free movement) and it seemed appropriate for the volleys to be used only at a range of one square (6").
The third change is to cover. When in cover the attacking range for all musketry is reduced to one square. So units attacking units uncover need to close with them and suffer an additional attack until they do so.
The fourth change is to the disruption rule which is used when a takes a hit, and also when rallying units. All units require a 3+ to pass. Line infantry when supported by another line infantry unit in an adjacent square add +1 to their dice roll, and light infantry/skirmish units get a +1 when in any cover.