Configure

You must proceed as if you where defining a line inside a User except the fact that this is done inside the Line tab of a shared profile.

Once the line defined in a shared profile, just link  users to this shared profile from the general tab of the shared profile

Go then to Account management / Users and edit the user (in this example user is Philippe Joliet) and open the Lines tab.

The small asterisk * symbol next to the inherited word means that the line is inherited with some fields values different from the defined values in the shared profile.

Editing this lines will show a screen like this one:

All grayed fields are inherited values while the 2 fields Default DDI and Default Global Line has been checked out meaning that these fields are rewritten in the user profile to the "Yes" value.

Change made from the turret interface is applied only to the user , not to the shared profile