“CorruptedString” (Solution)

Answer

You can use the internment mechanism:

var s = "Hello";
string.Intern(s);
unsafe
{
  fixed (char* c = s)
    for (int i = 0; i < s.Length; i++)
      c[i] = 'a';
}
Console.WriteLine("Hello"); // Displays: "aaaaa"

Problem