I just thought of something. Would a normal Sim founder be able to complete the Diving skill challenges then afterwards turn into a Mermaid and have them count?
I think the answer is NO, because once you create your founder's Life State as human, it must remain as human for the entire challenge. If you changed the founder's life state, it would invalidate the point of the challenge. If you want to do the diving skill challenges, you can't use mermaidic kelp, you have to remain human.
I didn't like the thought that "Oh, a skill is mastered already by being born a fish, you can't supermax it" because I was like "So a skill is mastered, isn't a supermax not just mastery of the skill?" but I think I get why they did that - mermaids don't just have mastery of diving, they have built-in Steel Lungs so they never need to surface, which makes the diving skill challenges easier. Of course, a human diver could declare Steel Lungs as one of their LTRs, but they have to earn it while the mermaid does not. So basically, mermaids are allowed to be a life state in the dynasty, they just are banned from using their diving skill at ALL.
Speaking of changing life states, I don't know if this was already asked and answered, but I have to ask: Since spares have no restrictions on changing traits or extending life, do they also have no restrictions on their life state? I mean, in an earlier attempt, I had a fairy founder mate with Violet Slymer and get two golden ghosts and a human. I had the human marry Ayder Van Gould and ask him to turn her before they married. I had married her out of the house so there was no vampire in the house but if I hadn't married her out, would her becoming a vampire have cost me the challenge? Just asking as I am currently thinking of making my two human spares for my recent attempt into a witch and fairy, but won't if I am not allowed to.