Enum DataValidationCriteria

// Change existing data-validation rules that require a date in 2013 to require a date in 2014.
var oldDates = [new Date('1/1/2013'), new Date('12/31/2013')];
var newDates = [new Date('1/1/2014'), new Date('12/31/2014')];
var sheet = SpreadsheetApp.getActiveSheet();
var range = sheet.getRange(1, 1, sheet.getMaxRows(), sheet.getMaxColumns());
var rules = range.getDataValidations();

for (var i = 0; i < rules.length; i++) {
  for (var j = 0; j < rules[i].length; j++) {
    var rule = rules[i][j];

    if (rule != null) {
      var criteria = rule.getCriteriaType();
      var args = rule.getCriteriaValues();

      if (criteria == SpreadsheetApp.DataValidationCriteria.DATE_BETWEEN
          && args[0].getTime() == oldDates[0].getTime()
          && args[1].getTime() == oldDates[1].getTime()) {
        // Create a builder from the existing rule, then change the dates.
        rules[i][j] = rule.copy().withCriteria(criteria, newDates).build();
      }
    }
  }
}
range.setDataValidations(rules);