It uses a scriptlistner version of save for web for both png8 and png24. To change the png24 so it uses a normal save and retains the dpi find this line of code "case png24Index:" It should be about line 840. Comment everything between that line and "break:", about line 890. Then add the following lines.
pngSaveOptions = new PNGSaveOptions();
pngSaveOptions.interlaced = dlgMain.pnlFileType.pnlOptions.grpPNG24Options.png24Inter.value;
app.activeDocument.saveAs( new File( exportInfo.destination + "/" + fileNameBody + ".png") , pngSaveOptions, true, Extension.LOWERCASE );
I have not tested this, you may also have to add checks for 8bit, no extra layers, no alpha or spot channels, etc. SFW does most of that by default. But by using the saveAs method and setting copy to true I think it will be ok.
