1. Currently the game handles armor penetration based on a single target property: bulletPenetrability (in the BISURF file).
2. Composite armor and ERA could be *easily* and *accurately* handled by introducing a second penetrability type, say "HEATPenetrability".
3. A corresponding CfgAmmo property would be added as needed, identifying whether the projectile should use HEATPenetrability instead of the default bulletPenetrability, e.g. "HEATPenetrator = 1;"

This way the feature only takes effect if new content is added. Existing content is unharmed.