Well, perhaps it's a silly answer, but the first possible mistake is "roman Triarii" instead of "roman triarii".

The second point is that I cannot see the need for a background script only for this purpose. It would be enough with a normal trigger in export_descr_advice, as in Client Kingdoms mod.

Third point: Did you try the final script without the authomatic "button pressing"?

You should include some "mark" just to know where the method is failing.

Good luck!