This works for all AGE games...
This less complex as it seems if you want to edit the name only for cosmetic purposes, as you can change this directly into the LocalStrings_RED file with Excel...
You have to change (in English) in Column B the content of the cells in the rows that hold the Model_Name_xxx, Model_ShortName_xxx, Unit_Name_xxx and Unit_ShortName_xxx, and once done save and replace the file in csv format.
Note however that this won't change the name of the said leader in existing scenarios, because the name has been "written" from the original DB when creating the scenario. However, your new name will appear in the tooltips and units details.
To have the new name permanent would require to regenerate all the scenarios and events where he appears
What is the purpose may I ask ?
