Custom form field

For a star rating form field would it be possible (using custom code) to change the value that is added to the data source once a star rating is submitted (for example, one star = not happy, 2 stars = okay, etc. )?

Yes, that is possible with custom code.
In order to do this you can open the developer options and paste the code below in the screen JavaScript.
You will need to change ‘Rating’ to your form field name on the second line, and in the ‘ratingCustomValues’ variable, you would need to replace the values next to the numbers with your values to be added to the data source. Zero value will be saved to the ds if the rating field is not required and not selected.

//this is the name of the form field -> change it to your form field name
let ratingFormName = 'Rating';
let ratingCustomValues = {
  '0': 'Have no words to describe how bad it is',
  '1': 'Terrible',
  '2': 'Not that good',
  '3': 'Neutral',
  '4': 'Good',
  '5': 'Excelent'

Fliplet.Hooks.on('beforeFormSubmit', function(data) {
  let newRatingValue;
  if (data[ratingFormName]){
    newRatingValue = ratingCustomValues[data[ratingFormName]];
    data[ratingFormName] = ratingCustomValues[data[ratingFormName]];
  } else {
    //0 option will be saved to the ds if the fields is not required and not selected
    newRatingValue = ratingCustomValues['0'];
    data[ratingFormName] = ratingCustomValues['0'];

Hope that helps.