I clearly stated that "modifying them through the characters file do nothing and only works for non-famous/great families", explicitly precluding modify the names under the family header in the respective culture files.It is in the culture files located here:
\ImperatorRome\game\common\cultures
Modify the names under the family header in the respective culture files.
Modifying the family headers of great families in the culture files, such as Lagid, Magid, Antipatrid, and Antigonid, do nothing whatsoever.