You are able to create tiles that can be fired through without breaking that tile. You can fire through windows without breaking the glass (at least, I can on my custom-made window)
AFAIK, the issue lies with the restricting of vision. I believe the reason you can shoot through windows is that they have the “TRANSPARENT” flag. If you remove that, I believe it can no longer be fired through.
So currently, again, to the best of my knowledge, you cannot create a tile that both blocks sight and still allows rounds to be fired through it.
EDIT: I also plan to have a “let’s mod Cataclysm” youtube series, but that won’t be up until the end of January, and I’ve been learning as I go. If you have specific questions, there are a lot of helpful folks in the forum, just ask.