Hi all,
Just made a video about how to reharmonise a song. It essentially involves changing the chords and/or melody of a song while taking the harmony (interaction between the melody and chords) and structure of the chord progression into account.
There's also a link to a google doc that lists all possible reharmonisation chords for all 12 notes in the description.
Check it out if you're interested.
Cheers
How to Reharmonise a Song