Various notes regarding the import/export mechanism and assorted questions asked above...
1. We have a formal XSD for the import/export file structure. One of the tasks on our todo list is to properly annotate it with explanations of everything. My guess is that it will be another week or two before that gets done, though.
2. Anything to do with the XML structure can be freely discussed here. Even if it's something we shared privately with the Beta team prior to release. The XML structure is intended to be a public format. We just haven't gotten it documented yet.
3. When we designed the import/export mechanism, we never considered the use case of someone repeatedly importing material from another source. We figured that content would come in and then potentially cycle back and forth with another tool, but we never envisioned continually importing from the same source - which is what @Farling is doing with Obsidian Portal. Consequently, there is nothing in place right now to handle the one-time generation of uuids that can subsequently be re-used. This is something we'll need to consider and solve in the future.
4. The "original_uuid" and "signature" attributes are something that should NOT be used when importing from another source. They have a very specific use in conjunction with import and are for internal use only - at least, until we get a chance to re-think #3.
5. The uuids used by RW are of the same general format as standard guids, but their composition is unique to RW. If you generate your own uuids, you absolutely run a risk of rendering all your data unusable due to the uuids being invalid.
6. Use of uuids not explicitly generated by RW will present the opportunity for errors, and the validity of uuids is critical to the proper operation of RW. Consequently, we won't be sharing how the uuids are generated. The only real possibility here (that we've thought of so far) is to enable RW or some other tool to generate a block of uuids that can subsequently be used.
7. Generating uuids from one realm and then using them for other content in a different realm is going to create a vast sea of problems that even risks contaminating other realms in the database. Please don't do that, as the results could be disastrous.
I have a suggestion for how you might work around things on a temporary basis that I'll post in the Beta forums. It's something that would maybe work now, but it will NOT work in the future, so it's not something suitable for posting here. A proper long-term solution is needed for #3.
Hope this helps!