Does being a principal mean you can change the whole school?

NO. A principal and teachers are hired by a School District and they must do what ever the School District tells them to do.

principles are hired...like prison wardens because of their track record, the ability to make the institution money, and their rule following ideals

No. A principal in a public school is there to enforce and administer the rules approved by the Board of Education for that school district.

If you want to create your own school, that can be done. It is called a private school or sometimes it can be done as a charter school or magnet school. Charter and magnet schools often have different curriculums but are still under the umbrella of the school district. If you have a curriculum, methodology, etc. and a can get enough support from others to get a charter for a charter school or financial backing for your private school, you can open one. To realistically get students to such a school, you'd still need to meet the state board of education's requirements and become accredited.

Gwen is correct, and even if you became the superintendent, the school board and administration are there to split the power and control. You can still become a principal or superintendent, your ideas can be brought to the board for discussion. But there is not a way that you can make all the rules without discussion.

The principal doesn't make the rules. The superintendent of the schools does that, along with the school board and administration. You'd have to create and operate your own school.