This was requested a while ago; I forget by who (sorry):
The stronger vassals bonus is the same bonus I wrote for my Topkapi Palace Wonder.
This really isn't meant to be used stand-alone but for modders who want to include new traits outside the traditional XML bonuses.
All the python is labeled and searching for 'Inf Trait' should find the changes.
I recommend downloading and using Winmerge to combine python.
Influential Trait (XML+Python) 2016-10-05
Influential Trait (XML+Python)