This is a solution described in the forum post. The blog is basically for making the related codes be more searchable.
The built-in dialog of [Export] is not customizable currently. While the API provides an object FileDialog that can be a workaround. i.e. make your own Export dialog and specify the parameters you would like to have such as file path and file type. This dialog is still a traditional type. I will write another blog on how to make an HTML dialog like the same style of built-in Export dialog.
import adsk.core, adsk.fusion, traceback
def run(context):
ui = None
try:
app = adsk.core.Application.get()
ui = app.userInterface
filedlg = ui.createFileDialog()
filedlg.initialDirectory = '/Users'
filedlg.filter = '*.f3d'
if filedlg.showSave() == adsk.core.DialogResults.DialogOK:
design = adsk.fusion.Design.cast(app.activeProduct)
option = design.exportManager.createFusionArchiveExportOptions(filedlg.filename, design.rootComponent)
design.exportManager.execute(option)
except:
if ui:
ui.messageBox('Failed:\n{}'.format(traceback.format_exc()))