Is the basic principle of Pat Martino's Diminished Concept for chord construction anything more than simply altering diminished chords?
The so-called diminished concept is just a way of memorizing the shapes of the four inversions of dominant seventh chords by lowering one of the four notes of the diminished chord.
By its symmetrical structure, the four inversions of the diminished chord have the same shape on the guitar, that's why they're easy to remember. This is not the case with other seventh chords (and other 4-part chords in general). The special thing about the dominant seventh chord is that it can be easily constructed from a diminished chord by lowering one note. E.g., from an Edim7 chord in a drop-2 shape on the top four strings
X X 2 3 2 3
we can easily construct the four dominant seventh chords
Eb7: X X 1 3 2 3
Gb7: X X 2 3 2 2
A7: X X 2 2 2 3
C7: X X 2 3 1 3
The additional chords can be generated by altering other degrees of the chord, such as is discussed in Where can I find a complete list of 3 note Freddie Green jazz chords?
Further discussion of the Pat Martino "Diminished Concept" aka "Sacred Geometry" can be found at http://www.patmartino.com/Articles/GuitarPlayer_April_2004.pdf