Change the Saved Track Defaults to characteristics you desire, then any "new" imported track will have those characteristics.
Other than that, you have to individually edit each track to have different characteristics.
But, you can use Reefmaster to merge individual tracks into one track with track-segments. At one time I have over 45 individual tracks for boat-runs, roadbeds, creeks, etc. I merged all roadbed tracks into 1, boat-runs into 1 & creeks into 1.
Roadbeds I make color black, boat-runs I make green & creeks I make blue.
Saves alot of time after a Restore Defaults or Software Upgrade. . . .