I have defined the naming standard for a NOT NULL Constraint in Design Properties (double-click the design name, Settings-> Naming Standards -> Templates) like this:
How do I get my NOT NULL Constraints named as defined in the Template?
Check your Preferences.Generate Short Form of NOT NULL Constraints must be turned off.
Then select the relational model from the Browser, right-click and select Apply Naming Standards to Keys and Constraints.
Make sure to choose Not Null Constraints.
Now you can see the names defined for the not null contraints in the Column Properties.
You can also see them defined in the DDL Preview.
And in the DDL itself.