Changing scores, comments, or any other content generated by the users is not a good idea and is not recommended by HappySignals
Yes, there might be cases when the user gives you a negative (or positive!) score unintentionally by mis-clicking a wrong score or by misunderstanding the scale. But these are droplets in a sea and very rarely have a real impact on the big picture. You should be concentrating on the broader view and improving the services. Also keep in mind, that contacting the end user about a wrong score after some time has passed, might already have an effect on a person's mind, and they can be more conciliatory towards the case, which can skew the actual experience.
Also, another issue that arises from touching the scores is trust. If it is known that you have the ability to edit the scores, the trustworthiness of the data decreases rapidly and your stakeholders will start to question the metrics. This is also the reason why this is not possible in HappySignals.
However, if you bump into this situation, what you can do is report them separately. E.g. if you are the owner of a low-volume assignment group or something else more granular where singular responses might have an effect, and a mishap mentioned above has occurred, you can add it as an exception in your stakeholder reporting and explain the case transparently.
Also, you can use the tagging system on the HappySignals feedback page and mark the response with a descriptive tag.