Thought I'd share this one out, since none of the questions I've made through the years in this forum have ever been answered to any kind of satisfaction, which could simply mean that as a guy who uses regularly three or four different OS's I ask weird stuff from the "apple only" point of view.
Then again, it could be my karma.
Anyway, here's how: under Applications/Utilities there is an application called "Directory Access". Inside you will find the settings for SMB/CIFS. SMB is the subnet's domain/workgroup. Unlock, doubleclick, type new name, accept, save, "apply".
Take care and thanks for trying and the moral support.