Add More Tracks to a Mod Package

I have an Indycar series mod to force rolling starts and lower caution thresholds, since I often saw cars spin out on ovals and not cause cautions to be thrown. I recently downloaded more tracks and want to add them to the mod package. When I try to update the mod, however, the 'Package' button is greyed out. How can I edit the mod to include the new tracks?

 

You have to create a new mod. Adding to an existing mod doesn't work.

 

Is there any way to enable a mod for all tracks then, so I can add more in the future without rebuilding every time?

 

No