The PI should contact NSF IT Help Central (ITHC) and/or the Program Officer if they wish to submit through Grants.gov and provide additional Units of Consideration. They should get direction from ITHC and/or the Program Officer on how to move forward based on that guidance before submitting the application. Any time there is a question, the PI should reach out to ITHC and/or the program office to ensure that they have the latest guidance.
There are many updates that can be made through proposal file update within Fastlane after a submisson but this is not one of them.