I've not tested this so it's possible I'm missing something but there would be two ways. The first would be to create a new .pack file which had a table in trait_level_effects (renamed to something else) which changes the number to 0 and run that as a mod after optimising it.
The second way I'm not so certain on, as I haven't done it before for traits and I might be missing another table reference somewhere, would remove any reference to it. For this you would need you to delete the whole key from any mods you have which edit that key, and create a new instance of the trait_level_effects with the same name which has the key removed (and will overwrite the existing table with the same name that CA uses in your game). To delete the key (using PFM) find the line that has the trait "r2_sp_trait_all_likes_greeks_1" with the effect "rom_building_culture_conversion_hellenic" and select the row number on the far left and press the delete key, then save.
I was going to put up a .pack file of it for you but since it would cover more options, here is a quick PFM tutorial of how to do it and I'll use DeI as it already has a table that overwrites CA's one (by having the same name). I'll show you removing the key though you could just set the value to 0 and save too, but they'll still have the effect that way it just won't do anything.
First, open the .pack file you think includes or edits the likes greeks key:
Then open db and scroll down to trait_level_effects:
Create and enable a filter to find the likes greeks key (or just look for it):
Select the line:
Delete and save:
In case you're not using any mods that change the value and want to make a mod that removes it from the base game, start by clicking filee -> my mods -> new and including data_rome2.pack in the window that comes up and selecting the same trait_level_effects table. Edit it the same way and make sure to file -> my mods -> install ModName after saving your new version and then enable it in mod manager.
Sorry it's a bit rushed I remembered half way through I need to run out. I hope that helps though.