Even if you do not change the information on the back side, the extension confirmation received by email is still legal.
The immigration officie already change the inforamtion in the system.
If you wish to change the content on the back side, you can change it by going to the immigration office directly after applying on the Hikorea website.
2021.6.10
* Notice: The regulation could be updated anytime by the Korean government. If you have further question, please check on hikorea.com