Manipulating Public Opinion calculations

[Ablatt_Ross]

"If (civ) adopts an ideology that is not preferred, the effect on Public Opinion from Civilizations with the preffered ideology is halved."

I've been sifting through endless civ5 lua references and have found very little to do with Public Opinion/Ideology tenets.

Basically, is there are a way for me to manipulate the calculation done (tourism v tourism) that generates the negative public opinion of an un-preferred ideology? Or is my recollection of how Public Opinion/Tourism/Ideologies work slightly off? It's been a little while since I've actually played far enough to experience it.

Thanks