list.ForEach(delegate(Info i) { if (i.Postcode.StartsWith("HR")) i.SomeProperty = true; });Or, more reusable:
private static void MarkPostCode(Info i, string s) { if (i.Postcode.StartsWith(s)) i.SomeProperty = true; ; } // used with: list.ForEach(i=> MarkPostCode(i,"HR"));