This is a follow-up to the previous one.

Instead of alternating I and IV in a pattern you add sort of a V minor 7 chord.

Sounds like blasphemy? Well it works, because all the notes you’re playing in this riff are part of the mixolydian scale of the I chord.

You do NOT move to another mixolydian scale.
You are NOT changing chords in that sense.

Although you could argue that you are playing a full IV chord and a V minor 7 chord, try to hear them as extensions of the I chord – because they are.

The Bb7 chord contains Bb, D, F and Ab.
The Bb mixolydian scale contains Bb, C, D, Eb, F, G, Ab, Bb.

The notes you’ve added with these “IV and Vm7” chords are (check the TAB) Bb, Eb, G for the IV chord and C, Eb and Ab for the V minor 7.
As you see: these are all notes from the mixolydian scale of Bb.

Note: the IV chord we’re using as an alternate to the I chord is not a IV7 chord.
This 7th (a Db on the IV chord Eb) is from the Eb mixolydian scale and would suggest a different harmony.

Move this pattern up 5 and 7 frets to get the corresponding riffs on the IV and the V chord.

The same type of accompaniment can be played in the 1st Blues position.
Again we’re using the inner logic of the mixolydian scales to move to the IV and V chord patterns.

Keep your thumb wrapped around the neck with these examples.

Try to play only the top three strings on the IV and V chords, they sound the best and give you a change from the sound you get on the I chord.

Experiment with hammering on the added “chords”.
Try, for instance, to hammer on that V minor 7; your grip on the neck is pretty tight and you only have to add your middle and ring fingers.

Also play around with “scratching” the up strokes, meaning keep your left hand on the strings and damp them while you play an up stroke.

Have fun and keep the groove goin’.