Ah no, BI does not overwrite vanilla files (and neither does EB), it sort of acts as an add-on, whereby a seperate .exe tells the game to access different files (BI files) instead of vanilla files. BI files are 1.6, but vanilla files are still 1.5. This is roughly similar to how EB works at the moment. All its files are installed in a seperate folder in the RTW folder, and we use a shortcut with the command line -mod:eb to tell the RomeTW.exe to look in the EB folder for files rather than the vanilla folder. The great thing about this is that you don't need a seperate install of RTW to play EB and vanilla (though other mods that don't use the -mod: command will need a seperate install as usual).

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