when I tested adding the reforms to BI it seemed a non-roman faction could actually trigger the reform by building the huge city level building in a province with the 'italy' hidden resource (you can look up which provinces have that in your game in descr_regions.txt). I'm not sure in RTW if it would have to be roman culture that builds the huge city or not.

Hang on to your save in-case you have to go back, but try getting one of the relevant cities up to huge_city and see if it works...