> I was not aware that removing a single character would warrant the
> addition of a copyright header.

I am not aware of any policy about this in the Guix project. But, I have
seen people do it both ways -- both adding and not adding copyright
headers for trivial changes. So, I generally add copyright headers for
all changes no matter how trivial.

> I have made less trivial changes in the past and I have never added a
> copyright line.  Should I do something about that?

I think you can ignore those instances. Even I have made trivial changes
before and not added a copyright header.