I got my information from LT Jordan Fogler, Plans and Programs Manager from Office of Admissions in charge (for the last time, as he moves on) the CVW program. The exact question of the OP was asked in a Q&A to LT Fogler in front of many, many folks and kids.
So it is permissible to Contact Admissions to Update SAT/ACT for NASS. (BTW, Army's SLE program uses an update-able portal for the USMA equivalent of the NASS)
The Acceptance Email sent to an NASS applicant provides the email of a respective Regional Admissions Counselor designated for the NASS region he/she comes from. My DD's NASS Regionall Admissions Counselor is also my DS's USNA Regional Admissions Counselor for Class of 2020.
time2, I think the proper context for that statement you pulled up is relative to the act of hitting the "submission" button for the NASS application once filled out and ready to go. Unlike a 'real' Admissions to USNA Application in a portal, the NASS is not using an update-able Portal. So in context, yup, ONCE AN APPLICATION IS SUBMITTED that's it for doing it again with that Form.
What it says in full from the Grey Box:
Ensure that you verify the accuracy of your completed application and print a copy for your records prior to submitting.
When you select “Submit”, the application module will check your data entered for format errors and confirm your desire to submit an application. Continue the submission by confirming.
A message in green letters that reads “SUCCESS” will confirm your successful submission of an application.
THE ABSENCE OF THIS MESSAGE INDICATES A FAILED SUBMISSION.
ONCE AN APPLICATION IS SUBMITTED, GRADE INFORMATION, TEST SCORES, AND EXTRACURRICULAR PARTICIPATION CANNOT BE MODIFIED OR SUPPLEMENTED.