Can't decide if this is a bug or expected behaviour but currently, if you don't select the Custom naming option when creating multicam clips, you aren't able to change them later.
There are a few issues with this. What if you don't know, or simply forget to select Custom, perhaps an edit assistant made them.
Even if you do select Custom, Premiere creates them in a seemingly random order, which makes adding scene/take info to hundreds of dailies no fun at all.
[Update - I've discovered selecting Audio Clip Name (not Video) allows the clip name to be changed. So, still a bug but there is a workaround]