Sorry, but I'm not entirely clear about what improved 'efficiency' you are trying to achieve.
If you save the Diagram with the coloured direct line link as a Family Historian Chart, then it is easily displayed at any time.
It is not a 'frozen' Diagram, so as data and people are added to your Project the FH Chart will update.
What do you see as being gained by displaying a Diagram with some marker such as stars against the same direct line?
A simple option would be to add an Individual record Flag to those direct line Individuals.
Then the Diagram > Options > Boxes tab lets you apply any Box Feature to just those Individuals that have the Flag.
The feature can be an Icon or Box Colour, etc.
There are also functions such as =IsAncestor(...) and =IsDescendant(...) that can be used to determine the relationship between each Individual and a nominated root Individual. They can similarly be used in the Diagram > Options > Boxes tab to conditionally add any Box Feature to just those Individuals who are direct line ancestors/descendants.
The advantage of this use of functions is that they automatically adapt the Diagram Boxes as new direct line Individuals are added to your Project, whereas record Flags (or your idea of stars) must be manually updated as Individuals are added.
See FHUG Knowledge Base
Using Icons for further guidance on Icons and other Box Features.
