That's why I suggested just a handful of options that are determined beforehand. We could tailor them to be the most easily understandable options. It's not full customization, just a few extra options. Sure Centurian might be a little too esoteric but I don't think people will have a hard time understanding that a "colonel" or "brigadier general" outranks them in the military.
We already do it this way for lordship titles and no one seems to get confused by that.