Changing a nickname is sort of like a single woman who changes her last name when she gets married. It does not fundamentally change who she is, we just use a different name to address her.

So, editing an existing expense nickname will not do anything to the underlying data. Everything previously associated with the old name is now associated with the new name. It will however, not be able to tell you what the name used to be before it was changed. For the vast majority of my customers, this is not a problem and I would say go ahead and edit them if it will make your workflow better.