Blackberry Blossom has a lot of chord changes. Navigating those changes with vamping is a great workout for your fret-hand, and even better for your understanding of fretboard layout. In this one we'll use a combination of root shape chords and 1st inversion shapes so there are less large shifts required. The licks will show you more to navigate the same changes with different chord shapes. Knowing common chord shapes and locations can really equip you with the fretboard knowledge you need to be a better lead player.
The B section uses 1st inversion, 2nd inversion, and root shapes to make the backup a bit more interesting and give a sense of movement while playing over the E minor chord. This pattern will remain the same anytime you are vamping over a minor chord. They are movable shapes. Whether playing major or minor chords there are essentially only 3 basic shapes to learn and memorize. So much of Scruggs style banjo playing is based out of chords. Knowing your shapes is important!
Whenever a song calls for a 7th chord you can always just play the basic chord instead. The licks will also show you some options to play actual 7 chords.