Over at XDA, forum member 'kwbr' has linked to some guides (hosted by HTCPedia) that were published for Microsoft's TAP or Technology Adoption Program. The guides themselves are quite lengthy and go into much detail revolving around three core areas: development, architecture and customization and are related to an earlier leak on WP7 architecture (read here).
Of most interest for the tech-savvy (e.g. tweakers, ROM chefs) would be the one pertaining to device customization. Perhaps of little surprise to our audience, but Windows Phone 7 evidently has a registry for manipulating many areas of the OS (startup screens, languages, start tiles, default ringtone, camera modes, etc.).
This may mean at some point an on board registry editor might be able to manipulate these values to do what we do now: customize the UI to our liking, at least within certain limits. However, there could be one obstacle: the registry might be locked down or inaccessible. Still, assuming access, Microsoft has done all of the work for us already by documenting these changes and showing their relative parameters--as opposed to the current "hunt and peck" method that we've been using for years.
The material is dated by a few months, so information has probably changed. Still, it provides some useful data for those who want to know.
Download PDFs below; Read original XDA thread here.