Mutate C# strings

Program.cs

using System.Runtime.CompilerServices;

// An "immutable" string
var x = "I am immutable";
// *Insert evil laugh here*
var y = Unsafe.As<char[]>(x);

var z = "mutable!!";
// Overwriting the string
// Might only "work" on x64 but for hackers 'Might' is good enough ;)
for (int i = 0; i < z.Length; ++i) y[i+3] = z[i];

// Prints "I am mutable!!"
Console.WriteLine(x);

Program.fs

open System
open System.Runtime.CompilerServices

let x = "I am immutable";
let y = Unsafe.As<char[]>(x);

let z = "mutable!!";

for i = 0 to z.Length - 1 do y[i+3] <- z[i];

Console.WriteLine x

Program.vb

Imports System.Runtime.CompilerServices

Module Program
    Sub Main(args As String())
        Dim x = "I am immutable"
        Dim y = Unsafe.As(Of Char())(x)
        Dim z = "mutable!!"

        For i = 0 To z.Length - 1
            y(i + 3) = z(i)
        Next

        Console.WriteLine(x)
    End Sub
End Module