field overwrites

Is there a way to not have the script push data to hubspot if the contact has used the form before?

Here’s what I’m looking for.
When the user first completes the form, I add a dynamic user number.
I’d like that number to always exist.
If that same user comes back and fills out the form again, I’d like to not push that one field and “update” the user number. Can you add a function that checks for an existing value and in the form settings allow for me to select which fields can be updated and which can’t?

Hubspot currently does not allow for that functionality.
Any submission overwrites any existing data.

Thanks!