What Alan said. Most of what constitutes the v4.0 upgrades are graphical in nature, and GMT will be doing their own graphics. There will be some (fairly minor) rules changes, but these were always intended to be incorporated into the "Rising Glory" games -- and most of those aren't actual "changes," per se, but rather tweaks to improve clarity.
None of the existing Nappy20 games will require redesign because all these changes are fully compatible with existing systems/components in previuos games. In point of fact, all the rule changes have already been "leaked" here on BGG: you can read through the discussions in the various Nappy20 and "Rising Glory" folders here on BGG.
Hope that clarifies things a bit.
Lance McMillan Developer for VPG's "Napoleonic 20" series
I just want to commend and thank VPG and everyone associated with this 4.0 rule change. You've handled this with incredible grace, customer service, and intelligence. It seems like it should be merely expected, but all too often customers get left behind in the rush to upgrade and improve. Victory Point Games...Hurrah!