How to change the behavior of a field that extends Shared Region in OAF Page via customzation?

Hi all,

When creating a new customer in Receivables, we want to create an account first by User A, and then create a site by User B, but some fields ("Site Number" and "Country") are mandatory, so can't save by User A.

I tried to implement via OAF Personalization, but found "Required" property is hidden on Personalize Page.

I had checked the Region definition for this Page and found these 2 fields extend an Shared Region, Oracle support tell us this can be done by OAF Customization, could you please give me some suggestion for this? which VO/EO need be customized? and how? thanks.