About selecting the Primary Run while creating the submission file

Hi, I have question for the Primary Run function while creating the submission file.

I understand that I can only select one of the Run to be my Primary one,
but is it possible to select the Primary Run(Primary submission) after I submit the file?
Or should I decide whether this submission would be the Primary Run before I submit to know the test accuracy?

It would be convenient if I could select the Primary Run after all the submissions.
Please let me know whether it is possible or not.
Thank you.