Hmm... let me be more specific, I don't think I was...
What I was thinking (and didn't explain very well) was that it would do something like this;
I understood you perfectly.
How it works now (bugs and missing bits aside)
1. You load the editor, it loads in the base unmodded database in the background. The base database is NEVER changed, it creates a duplicate and the duplicate is what everything that happens thereafter happens to.
2. You add a few techs, they are added to your duplicate database. You delete a unit, it's deleted from your duplicated database.
3. You spot a mod called '10 new units, 6 new techs and 30 new wonders!' and unpack it on your harddrive.
4. You go to the open dialog, and go into the XML directory and multiselect 'UnitA.xml', 'UnitB.xml' and 'UnitC.xml'
5. UnitA, UnitB and UnitC appear on the toolbox palette as unassigned units after the xml files you loaded are integrated to your duplicated database. As long as the xml your loading up is separated sensibly, then you can load or as much of the mod as you like.
6. You open UnitA's properties, change his icons and stats.
7. You drag the units onto the techs you want to unlock them.
8. You save. It pops up the conflict dialog, saying that UnitA goes obsolete when it hits one of the techs from the other mod that you've not loaded into YOUR database, and gives you a drop down box of all techs in your mod, to ask if you'd like to reassign it to.
9. It pops up another warning, saying that UnitB upgrades to UnitD who's not in your mod, and gives you a drop down of all the units in your modded game to select what he upgrades to instead.
10. Once all conflicts have been resolved, it compares your duplicated database against the unchanged base one, and based on the differences it generates you (at the moment one, but ultimately a few) XML files with just the changes necessary to take the
unmodded game to 'where it is now' in your database. 'Where it is now is a combination of stuff you've loaded and stuff you've edited, added and deleted in the editor, it's all completely transparent.
Once a mod, or part of a mod, is loaded into the editor, then it's ties to that mod end, it's just changed data in your updated database to be saved out as
your mod.
;D