In the .ini you can change the following settings:

* Fixed Start
* Roll Level
* Roll Sex
* Roll Race
* Roll Birthsign

The four "Roll X" settings define if that aspect of the character will be randomized. 1 means Yes for randomization, 0 means No.

Fixed Start allows you to enter a value between 1 to 100 to always have the same start. The description in the .ini explains how this setting works in more detail.
Use the numbers in this article to get a specific start (SPOILER for the possible starts): https://www.nexusmods.com/oblivion/articles/44522