The offline Character Builder had some houseruling support, but it was somewhat limited and the new online Character Builder has even less. Even if you have a fully legal character, some powers, feats, and items aren't quite properly handled by the Character Builder anyway.
Still, the Character Builders themselves are very handy for quick and easy character generation and computation of stats and such. Plus, the DND4E files are accepted in several tools (iPlay4e the most notable among them) as methods for uploading/importing character data.
So, the question then arises as to how we can manually edit the DND4E files to properly apply houserules and fix official rules that are broken.
Has anyone written and posted a guide online for this already?