Example patching script for binary executables written in PowerShell and running from a cmd batch file

patch_binary.cmd

@powershell.exe -ExecutionPolicy Bypass -Command "$_=((Get-Content \"%~f0\") -join \"`n\");$script=$_.Substring($_.IndexOf(\"goto :\"+\"EOF\")+9); &([ScriptBlock]::Create($script)) %*"
@goto :EOF

# PowerShell script starts here, we can also pass parameters like this since they are passed to the script block
param($parameter1, $parameter2, $parameter3)

$fileName = "game.exe" // game file
$fileHashString = "abcdef12345678901111111111111111" // the file's MD5 hash

function To-Utf16 {
    Param ([string]$EncString)
    return ([system.Text.Encoding]::Unicode).GetBytes($EncString)
}

function To-Utf8 {
    Param ([string]$EncString)
    return ([system.Text.Encoding]::UTF8).GetBytes($EncString)
}

$FileHash = Get-FileHash $fileName -Algorithm MD5
if ( $FileHash.Hash -ne $fileHashString) {
    Add-Type -AssemblyName PresentationFramework
    [System.Windows.MessageBox]::Show("Incorrect game file! The patch is for ... game.", "Error")
}
else {
    $bytes  = [System.IO.File]::ReadAllBytes($fileName)
    if (-not [System.IO.File]::Exists("$fileName.bak")) {
        Rename-Item -Path $fileName -NewName "$fileName.bak"
    }

    # Example of multiple offsets replacement
    $offsets = @{}
    $offsets.add( 0x00111111, 0x01 )
    $offsets.add( 0x00222222, 0x02 )
    # ...
    foreach($key in $offsets.keys)
    {
        $bytes[$key] = $offsets[$key]
    }
    
    # example of group noping
    $offset = 0x00333333
    $n_nopes = 5
    for ($num = 0; $num -le $n_nopes; $num++) {
        $bytes[$offset + $num]   = 0x90
    }

    # example of single byte replacer
    $offset = 0x00444444
    $bytes[$offset] = 0xEB
    
    # example of C-string replacer
    $offsets = @{}
    $offsets.add( "string1", "string_replacer" )
    # ...
    foreach($key in $offsets.keys)
    {
        $nreplacer =  $offsets[$key] -replace "\n", "`n"
        $nreplacer =  To-Utf16 "`0$($nreplacer)`0"
        $nkey = $key -replace "\n", "`n"
        $nkey =  To-Utf16 "`0$($nkey)`0"
        $bytes = $bytes -replace $nkey, $nreplacer
    }

    [System.IO.File]::WriteAllBytes($fileName, $bytes)
    Add-Type -AssemblyName PresentationFramework
    [System.Windows.MessageBox]::Show("Succesfully patched the game.")
}