Can we use same UNIQUE KEY more than once? (for same type customfield)

Can we use same UNIQUE KEY more than once? (for same type customfield)

What we want to do is, for example, we will take university info from the user in "1-step" registration.

Later, User can fill other fields in profile edit page but he/she will see University custom field under Education Tab.

If we can duplicate for example a dropdown custom field with its unique key, we can change both fields' view settings so that user can see "university field 1" in registration but cannot see when editing, instead he/she can edit same field on "university field 2" in the education tab.

Which code/file can we modify to make this happen?

Thanks