I am not OA consultant but I had to handle few personalization for an iSupplier implementation.I had a very basic knowledge on personalization, and explored few more stuff during this assignment.
I have used the below approach to create a new field in the OA Page.
Get the VO :
In any OA page, if you click on the 'About this Page' you will get clear idea on the underlying VO. Get the name of the VO and the column names. For the exact column name you have look in to the attributes table.
Create a new Item:
Click on the Personalize page link in the Page where you want to create a new field.
Select the respective region and click on Create new item icon.
Enter unique value in the ID, Prompt and some basic properties like read only, rendered, mandatory. The Item style as 'Message Text Input'.
The important part is View Attribute and View Instance.
In the view Attribute, enter the column name you want to store the value.
The column name is nothing but the attribute name you have picked by viewing 'About this Page'.
In the View Instance, enter the VO value. If the entered VO is not mapped in to the OA page, it will throw error message.
So make ensure that view instance and view attribute are appropriate for the page.
I have used the above approaches to create two new fields in the iSupplier Registration pages.