You can create a custom command in .tbr .men .rtb etc from a journal .vb file file as per below:
LABEL My Command
Can you do the same with favorites (.fav files)?
Found example in the OOTB .men file
BUTTON UG_INFO_SIMPLE_GEOMETRIC_DISTANCE PRIMARY=UG_INFO_GEOMETRIC_DISTANCE,FAVORITE="SimpleDistance"
LABEL &Simple Distance...
TOOLBAR_LABEL Simple Distance
MESSAGE Calculates the distance between two objects.
HELP UGS:: DlogUI::UICompMeasureDistance
No, favorites are specific to the existing NX dialog and essentially capture a particular state of that existing dialog. The favorite is like dialog memory for just the given dialog.