I'm thinking about starting a "trait dynasty" where the founder and spouse share a common trait (one that is available to each Sim at birth) and all the immortals will be born with that same trait. It's still following the same exact rules/requirements, but all immortals must be born with the trait. The mortals, may not have that trait at birth, but can either develop the trait overtime, or not develop the trait at all. I just thought it would add humor to the dynasty.
EDIT: I'm not trying to change the rules to the dynasty, or make up my own rules. I just wanted to try a story where all the immortals will do funny things, from their unlock interactions/idles/etc. Somehow the family would seem "normal." I might do this with the DecaDynasty challenge too.