This sounds to me like a kind of thing which is quite likely hardcoded in a client. It would be great if it wouldn't be so, but I'm afraid it is. Still, I am not sure.
The catch is that when you have a damage school, you also need to have a resistance against it. And that resistance needs to actually work, which means, that there must be a system handling it, and that system can be hardcoded just to fixed enum. Btw, elemental damage on weapons seems to not work on TC2. It worked on Mangos back in the day I was trying it (well, about 6 years ago), but it just never worked for me on TC2. Not on items, creatures deal elemental damage on TC2 as they should. It works from visual point of view, but deals no damage or just physical damage, I can't remember now. Rather test if even blizzlike elemental damages work for you, or not.