There doesn't seem to be a way to un-link them near as I can tell (and some scouring of the boards here seems to suggest it's by design), but I have found a workaround though through some trial and error after spending some 3+ hours scouring YouTube. It seems when you rename a track, the first channel tied to it changes as well. And vice versa: if you rename the first channel of an instrument, it renames the instrument track. But if you duplicate the track first, you should be able to rename the track or the channel without such trouble. then you can just remove your duplicated track.