You can assign macros to keywords in the [NavigationMacros] section to redefine the behavior of DITA2Go-supplied browse macros <$_prev> and <$_next>. For example:
[NavigationMacros] ; PrevMacro = content to put out for <$_prev> ; NextMacro = content to put out for <$_next> ; PrevFSMacro = macro to use for <$_prev> at start of file ; NextFSMacro = macro to use for <$_next> at end of file ; StartingPrevFSMacro = <$_prev> to use at start of first file ; EndingNextFSMacro = <$_next> to use at end of last file
See §29.3 Creating a browse sequence for information about using these and related settings.