It's a pain in the ass, but you really don't need the reference files to rebuild most of it.
Smart Exception + exe = dev.exe! Almost.
There are two new entries in the research prerequisite system.
916: Text FileArchive missing Label.
File: .\GameInfo\RESEARCHSUBJECT_ABILITYACCESS_ARBITRATETARIFF.entity
Label: RequiredFactionNameID
Line Number:16
Line Contents:MinimumArtifactLevel -1
Text FileArchive missing Label.
File: .\GameInfo\RESEARCHSUBJECT_ABILITYACCESS_ARBITRATETARIFF.entity
Label: RequiredCompletedResearchSubjects
Line Number:17
Line Contents:MinimumArtifactLevel -1
Thus we discover code for faction splitting in game! Any new functions in a new file, well... You're doomed there. But for now, much of the alterations can be discovered via file replacement. Stick the old diplomacy version in, and walla, it throws up missing lines and alterations.
Easy? Not in the slightest... Doable though.