You can use notes or you can put whatever you want on a non-printing layer.
Just a tiny suggestion.
If all you ever do is change the kerning or tracking, there's a setting in Preferences > Composition that allows you to highlight custom tracking and kerning.
The highlight is a tasteful green/blue that is easy to see.
Computer Graphics Trainer
Love that highlight. I'd love it even more if there was a way to know at a glance how much adjustment had been made.