Answer 1: yes, you can. To do this you should define a NotesNoteCollection with the wanted design element(s) and use it as input for your NotesDXLExporter. To set the wanted design elementes you could create the colelction and use the Add function to add individual design elements. You could also get all desing elements of certain type by setting the appropriate option and use BuildCollection.
Answer 2: you could parse it using the NotesDomParser. I would advice to have a look at the Designers Help for the NotesDomParser. The WalkTree is a good starting place.