The editors of the 4th edition of Napoleon's Battles Marechal edition (NB4) are giving in their official site NAPOLEON'S BATTLES Marechal Edition, some clues about the main modifications of the new edition. See below a summary
Marechal Edition Abstract
"In this new fourth edition, the order in which the rules are presented has been changed.
The rules are now introduced following directly the Turn Sequence, both in the Standard and Optional sections. The paragraph numeration has been mostly removed to adapt the rulebook to a less formal environment.
Moreover, a number of rule changes have been included, some of them regarding the Standard Rules and thus the basic mechanics of the game, and others listed as Optional Rules for players seeking a better degree of simulation, although adding some complexity to the game."
Measuring or not measuring, that's the question
Measurements can be taken freely at any moment
Moving and deploying in built-up áreas (BUAs)
The rules about movement and deployment in BUAs will be clarified and complemented with those for firing, combat and morale related to BUAs
New Firing procedure at Built-up areas
The authors make a series of considerations about the need of changing the rule of fire against BUAs. In their current state (NB3 and less), is too easy to rout or disperse an enemy unit garrisoning a BUA, only by fire (infantry fire inclusive!), as the authors show in a small statistical study.
This is in disagreement with history, where BUAs were usually the object of fierce hand-to-hand combats, before the enemy was routed. The need of a modification, was also supported by the late Bob Coggins himself, and the authors seem to propose one: "To fix this problem, we have changed the firing procedure for built-up areas, and after testing various solutions, we have chosen the one that, combined with a slight change of the combat procedure related to built-up areas, almost gives the attacker no chances of dislodging a deployed unit without an assault".
The authors do not reveal the actual new rule, so we must wait until the rules were released!
Watch this space!