Thread:GokūBlack10/@comment-24579076-20141020171009/@comment-1399043-20141020174802

Once you pass the exam, then you are free to develop your character further (ie: making them stronger) however you wish although it is recommended to do so with a story or in great detail as to how or when they obtained such power in their own backstory.

Now as for any "official" ranking, there isn't a unified Gotei 13 or anything like that as it hasn't worked out well in the past. You are able to make your character whatever position, rank, or level as you so desire as long as it doesn't ignore canon facts such as making a member of the original Gotei and saying they are stronger than Yama-ji (who was stated to being the strongest Shinigami in 1000 years and as such was the 1st and longest standing captain in the Gotei)

Hope this helps.