The LLBLGen Pro designer lets you specify output (code generation) setting values on a project level and on the element level. It can however become a bit time consuming to specify a setting for every element.
To help you with this, settings almost always derive their default value from default settings defined on the project level and which are edited using the Project Settings: The Conventions: Target framework settings and the Conventions: Attributes / Additional Interfaces / Additional Namespaces settings.
The easiest way to work with this is to see the convention settings edited using the Project Settings as the defaults for all elements in the project and the general way how things should work. Then, for every element which should get a different value for a particular setting or should get a different attribute defined on it for example, you should specify the particular setting in the elements' editor.
This way of working should give you the less friction and high productivity.