is there any way to write a script in Fm 4.1, that, on submission of a new record would check if there is already a record associated with that person and that document number but doesn't contain a review, and if so, to overwrite it and if not, create a new one?

Assuming that your record id field was totally unique for each person, then you would only have to specify that this field has to be unique at all times, prompting a warning before you overwrite it. That should be sufficient to disuade users from making duplicates. You can create your own custom warning windows if you want, though I have never done it.