The volume & pan labels have been recently updated. This conversation is very themeing-focused, but it helps us understand how things work currently:
https://forum.cockos.com/showthread.php?t=267524
The labels / readouts are not directly editable, like how renaming tracks ( .label) works. But that would be the best fit for everyone, I gather.
Perhaps it will come soon! Updates to themeing, and how that changes the behavior for users, seems important to devs lately.