Well, without any outside SOM assistance it will be impossible (that I know of) to make an item count in offensive and defensive.
In the .prf file, there is a section (I outlined it somewhere on here but who only knows where it is now) for all the stats: slash/stab/fire/water etc.
Just before the stats area is one hex that toggles the item type from weapon/armor...so unfortunately weapons and armor use the same file area to hold the stats of the items, it simply has a flag that says whether it will count as offensive/defensive. There is no third flag that allows you to split it in any manner unfortunately.
The + HP idea is a good one though.
I still wish I knew if there was anything special one could do with the system events that are in the first few slots of the map. I have a feeling they were put in for something special, such as if have item equipped, or maybe falling damage, but it looks as though From never utilized it for anything. Oh well.
If you do make an item that can double as a shield, just make an equivalent shield item for them to equip when they get the item.
