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I can save a 6 second preset for silence on one end of the wave but I can’t seem to save it for both ends at the same time.

I think you need to make a macro for that … Macros - Audacity Manual

Macro equivalent fro "insert silence"?

If the project has only one track, there’s a simpler way: SelectTime:End="-2" RelativeTo="ProjectEnd" Start="0" Silence:Use_Preset="<Current Settings>" ExportAs.... (Notice that “End” is set to negative 2, relative to “Project End”) For a single track in a multi-track project, one additional command is required (“Select Track Start to End”), and then select relative to the end of the selection (but this version would not be used for batch processing): SelTrackStartToEnd: SelectTime:End=…