Modifying setter argument - is it hack or not?

public void setString(String string) {
    this.string = string.trim();
}

object.setString(string.trim());

public double UserTemperature
{
  get
  {
    return Units.Instance.ConvertFromSystem(UnitType.Temperature, temperature);
  }
  set
  {
    double v = Units.Instance.ConvertToSystem(UnitType.Temperature, value);
    if (temperature != v)
    {
      temperature = v;
      Changed("SystemTemperature");
      Changed("UserTemperature");
    }
  }
}

actualVal = passedValue % 360;