Make a unique item for metal caps and take off the two original cap tags.
Oh, good idea. That never occurred to me. Unfortunately I've never tried to mod items before. I guess its off to the dwarf fortress wiki for me.
EDIT: Ok, I created a new item and attached the tag to my civ in the entity_default file. I basically copied the original cap entry and modified it slightly to look like this.
[ITEM_HELM:ITEM_METAL_CAP]
[NAME:cap:caps]
[WEIGHT:10]
[VALUE:10]
[ARMORLEVEL:1]
[BLOCKPOWER:20]
[LAYER:OVER]
[COVERAGE:50]
[LAYER_SIZE:10]
[LAYER_PERMIT:15]
[MATERIAL_SIZE:1]
[HARD]
[METAL]
If anyone sees any mistakes please correct me. First time I've tried editing items.
EDIT 2: Ran into a slight problem. [ITEM_HELM:ITEM_METAL_CAP] doesn't work and I had to change it to [ITEM_HELM:ITEM_HELM_METAL_CAP] in order for it to show up at the metalsmith's forge so I could make it. I made the item and was successfully able to layer it under a metal helm. So far so good. Thanks for the advice Johnny.