BLOCKCHANGE is only applicable to ITEM_SHIELD unfortunately, S'all in the wiki.
Hrrmm... Then I guess to have a blocking weapon I could possibly add the [SKILL:SHIELD] tag and achieve roughly the same effect. I remember a conversation where someone implemented "razor sharp wit" as a weapon and had them blocking arrows with it. I might be able to do something similar...
Has anyone tried something like this? All else fails I'll quickly whip up a test item and post the results to see just how effective such a weapon might be.
Initial tests confirm the obvious that you can use the shield skill just like any other weapon skill. I may have noticed more parries but I am testing to confirm this with an appropriate firing squad.
Due to the lethality of ranged combat, even when fully encased in armor, all 3 subjects suffered chipped leg/arm bones, leading to giving in to pain and falling down, leading to perforation, leading to death.
I may have to give them superior armor material than the bolts (or download that certain mod floating around that rebalances ranged combat) to see if they actually block the damn things with the weapon with any greater frequency than a normal weapon.