Would help me a lot if render(...) in HeadLayer:

Quote

else if (!(item instanceof ArmorItem) || ((ArmorItem)item).getEquipmentSlot() != EquipmentSlotType.HEAD) {
            float f2 = 0.625F;
            matrixStackIn.translate(0.0D, -0.25D, 0.0D);
            matrixStackIn.rotate(Vector3f.YP.rotationDegrees(180.0F));
            matrixStackIn.scale(0.625F, -0.625F, -0.625F);
            if (flag) {
               matrixStackIn.translate(0.0D, 0.1875D, 0.0D);
            }

            Minecraft.getInstance().getFirstPersonRenderer().renderItemSide(entitylivingbaseIn, itemstack, ItemCameraTransforms.TransformType.HEAD, false, matrixStackIn, bufferIn, packedLightIn);
         }

had some kind of prevention available, such as a new method in IForgeItem that prevents this from rendering too, something like boolean shouldRenderOnHead() with a default return value of true but could be changed

You could just subscribe to render player event and manipulate the layers/rendering or override the rendering.