You could use an Embedded Data field in the contact list to indicate they are a dual major student. Then in your Survey Flow, you can copy the block of questions that you want them to repeat, and create a branch logic to display it to only those students. So your survey flow would be:
- Set Embedded Data
- Question Block
- Branch if they are a dual major - repeat question block
- End of Survey
This will mean that students only complete the survey once, and you can simply merge your results together after the survey closes.
Alternatively, with the option suggested by @phbern above, you could present them with a retake link if they are a dual major student. If you set it up as a Retake as New Response it would allow them to record a second submission. You could then set the display logic that if the student is using a retake link (URL contains Q_R) then the retake link is not displayed to them, which would prevent additional submissions after their second one (for their second major).