21.60Your reharmonization toolbox so far

You now have:

1. Functional substitution

   • I ↔ vi/iii
   • IV ↔ ii
   • V7 ↔ vii°

2. Extensions

   • maj9, m9, 13, etc.

3. Inversions

   • create bass lines

4. Secondary dominants

   • E7→Am, A7→Dm

5. ii–V insertion

6. Passing diminished

   • C→C♯°7→Dm

7. Borrowed harmony

   • F→Fm→C

8. Deceptive resolution

   • G7→Am

9. Pedal points

10. Melody-driven chord choice

That's already enough to produce many sophisticated arrangements.