I think it depends on if you can justify it. For example, my character seems like she has more than one kekkei genkai. In reality she has one. The second is a natural evolution that came about due to a combination of her kekkei genkai and her genetic material. The third is a branch evolution, which manifested as she grew up due to how she was raised as well as her disorder. 

For the S-ranks, I think it is a question of IF you can justify it.