Important ranks?
You mean the ones that have access to clan functions?
How many people do you want deciding who can enter the clan and who cannot?
I suppose you could flood each rank with a range of ranks if you do not get the new feature. Then the player could denote on his bio which rank he is. Or leave it secret. Or perhaps as is common in the business world, due to cut backs, people now have multiple jobs they are responsible for doing...typically everyone does the work of 2 other people that have been laid off these days.
Rank 20: Acad, Genin, Chuunin
Rank 21: Jouning, special jounin, hunter nin
Rank 22: Medical nin, ANBU, ANBU Captain
Rank 23: Sannin, Kage, Village Kage
Rank 24: Master Kage, Grand Master Kage, Daimyo
Rank 25: Ramen chef, Sake House bar maid, Merchant
Rank 26: Gate guard, Courier nin, Street cleaner
Rank 27: Uzumaki Wannabee, Blondes, and Candy Stripers
Rank 28: Uzumaki Prophet, Profiteer, Politician
Rank 29: The Farmer and the Dell
Rank 30: The Cheese Stands Alone