Summary

1) Edit 3 files (add immortal trait only):
. "export_descr_character_traits.txt"
. "export_descr_VnVs_enums.txt"
. "text\export_VnVs.txt"
(i think engine must 1st parse enums file and then search text file for them)

2) Make shortcut like this:
. "RomeTW-ALX.exe -show_err -nm -mod:eb -noalexander"

No other changes (hence small download, or simply do it by hand).
Custom battles and standard imperial campaign should work.

As for "options +something" string in descr_strat i think it's a way to test all bi options separately (assuming that "options bi" enables them all) and mark the working ones. Had no time to test them yet.