Perhaps not so easy. There is likely to be a data structure that stores the count of units a leader has killed. The same count is used for both VotD and for XPs. For the idea to work there would need to be a second count stored, that of non-undead/non-mindless, just for VotD purposes. So far so good. The problem comes in the need to expand the size of a data structure to accomodate the extra info to be saved. This may have adverse side effects up to and including invalidating earlier savegames, depending on how IW has coded the program and what the data structures look like. Only IW can tell us how much work it'll be.
It's doable, but that doesn't mean it's also simple. Straightforward != simple.
