There is enough stuff out there to never stop learning-ever. From inversions, secondary dominants, sequences/melodic patterns, chord patterns, tonal center approach vs. chord per chord thinking, reharmonization.....the list can go on and on.
For inversions, you can learn to memorize them, or you can learn to transfer them via "string sets" and you can put different notes on the bottom- not just the root, 3rd, 5th or seventh.
Then you have slash chords, which are cool, and are much easier to notate than using all the alterations involved- and many players don't care for seeing an altered major 7th chord.
Modulations; you can think of pivot chords, using ii-V's to get there, Coltrane changes, secondary dominants- all the above......to use in a song or transfer from song to song like a melody of tunes.
Music is really endless. Duke Ellington, Mozart, Beethoven, anybody of their caliber-if they were alive today would still be studying and/or taking ear classes.
Hell, I can practice a la Thelonious Monk- one song for 5 hours. You CAN practice creativity.
