Silver Vulnerability for a Player Character/Feat.

So, to make a long story short, I have my own homebrewed rules for lycanthropy for player characters and I have decided to simply make them gain a "Curse" via a feat. However, i can't seem to find any way to give the player vulnerability to silver/silvered weapons without simply just writing it in the feat. I'd prefer if possible to have it display "silver" or "silvered weapons" in their defenses page. Is this at all possible?

yeah i am in your exact same situation, doesn't seem that the feat system allow for this... either all bps or nothing, you can't specify silvered, non silvered, magical, non magical when it comes to vulnerability, but, you can with immunity and resistance apparently

I know i am many years late, but what I did was I gave my players the vulnerability "Slashing from a Vorpal Sword" and in the source note put "Vulnerability to Silvered Weapons" so when they hover over it the Silvered Weapons part comes up