public class Sensor
{
   public SensorType SensorType { get; set; }
   public int RegisterAddress { get; set; }
   public int BitNumber { get; set; }
   public int Position { get; set; }
   public int Value { get; set; }
}

foreach (var sensor in sensors.Where(s => s.SensorType == selectedType))
  sensor.Value = newValue;

var list = new List<int>();
  for (int i = 0; i < list.Count; i++)
  {
    if (someCondition)
      list[i] = newValue;
  }

sensors=sensors.Select(x=>
{
    x.Value=x.SensorType==selectedType?newValue:x.value;
    return x;
});