Yeah, but that's the problem. There is no way to know all the relationships. This was an obvious one, there are a lot more subtle ones. In any case, the comments have been very helpful. A gradual implementation is the only sane way to go. Politics are not too big of an issue, if I can make a concise case and what's a better way to do it than a small project.
Documenting these relationships would potentially be a really, really valuable thing to do "going forward". It helps to make explicit things that are currently implicit, and possibly unknown. It then opens up the possibilities of making optimisations like using Linear Programming, but at the very least it reduces risk and helps to share knowledge.
