set up asset manager, Elfe has a guide on how to do it [Script][Basics]Modding Beginner's Guide I - #2 by Elfe
after the files are extracted you then just follow the steps on how to make your first mod (basically like a save file for mod changes)
then you go into the game tables in asset manager, and find the guns you wish to add the passthrough to, the guns have XY table IDs, you import those into your mod, then edit the value shown earlier, save, hit the build mod button, voila
*i know it might sound complicated in text form, but i promise you it gets much simpler once you actually sit down with Asset Manager and the game tables in front of you - i’m a luddite and was worried it would be too confusing, but i managed and feel like i got an ok hang of the basics now 
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