As I understand it, the rig name is what's displayed in the large font in Browse mode by default, and this can't be changed.* Personally, I find many rig names (Schmatz? Walking Moon? Revolution?) less helpful than the actual amp's name. In rig manager, I've updated the Amp Name field in my favorite rigs to change the frequently bogus names (MeBo, Fan, Mars, Goldie, Voice, etc.) to the real amp name and model. Now if I could only set the main display to show Amp Name instead of Rig Name in the large font...
*Please correct me if this is already possible!