Thanks so much. Many of my changes are based on the modes. A great way to do this is to know what the IV and V chords of the relative key to the mode you want to be in. Example, lets say you want to play in the G dorian mode ,then think of the IV and V of the relative major of that mode. Since G dorian is the same as F major, find the IV and V of F major or Bb and C triads and superimpose them over a G pedal tone Bb/G and C/G. This creates the perfect G dorian chord vamp. Notice that Bb/G is a Gm7th chord... Gm7 = G, Bb, D, F
Bb triad Bb,D,F. The C triad C, E, G are all in the F major or G dorian scale. Now try improvising over this progression with the G dorian scale.