Every chord or scale built upon given scale-tones has at least two available chords or scales that can be substituted for the original scale or chord. They mostly use chord substitutions. Well chords are only half of the story, the other half is scale substitution. However, most of the basic concepts of chord substitution do apply to scale substitution. This is a great technique for extending the value and color of arpeggios.
Lower neighbors are tones added just before an arpeggio tone.
In all cases they are one half step below the primary arpeggio tone. They are played as grace notes to the arpeggio tones. Therefore, they are played rapidly and resolve immediately to the primary tone. The result is very pleasant. Considering the large number of arpeggios, this is rather large challenge to attempt.