I downloaded and extracted the file from the link you gave, and then uploaded it to Paperpile using the Settings>Citation Styles>Custom Styles that I found in another thread about User Created Reference Styles, and then tried setting the reference style to that one. I cant remember exactly what wasn't right about it, but it didn't work as expected, so I then went back to the adamsmith link and spotted the revised file in the next tab. I then repeated the procedure as above which seemed to be slightly more successful, but I'm now having all these issues around 'need to reload Chrome extension' messages.
I have no idea about whether or not it is a valid CSL file either, I just assumed it was. What I would really like, in an ideal world, is just some simple way of choosing the types of the information I'd like to export - Title, Author (short form), Year, Abstract, and Tags (as individual attributes, not a collection). If this could be done using check boxes to modify as needed that would brilliant. From here, it feels as though setting this up as a reference style should be possible, but I don't know enough about either CSL or the inner workings of PaperPile to know if such a thing is possible.