In WinBB you have a Styles Menu

Save Current Song (except muted instruments) as a Style
Saves the style that is in use to the \bb folder with the parts that are currently selected. If, for example, a MIDI style
has had RealTracks added, the RealTracks will be saved with the style and the style name will get an = sign prefix.
So if you were to add an acoustic bass RealTracks to the ZZJAZZ style and save it with this feature, the name would
change to =ZZJAZZ.STY. It also saves MIDI SuperTracks and Hi-Q instruments (or other TGS files), and
automatically calculates dB offsets based on volume, taking existing offsets into account.
Press the [Rebuild] button in the StylePicker and the new style name will be added to the list of Other Styles.

In MacBB

Save Style As…
This lets you save a new style or edited style, or rename an existing style.

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Edit Existing User Style
Launches the StyleMaker with the current style selection loaded. This allows you to edit an existing style (*.Style) from disk. The resulting style can then be saved with the same name or a different name.