#include <APIResConstants.au3>
#include <MsgBoxConstants.au3>
#include <WinAPIFiles.au3>
#include <WinAPIHObj.au3>
#include <WinAPIRes.au3>

Global Const $g_sExe = @TempDir & '\MyProg.exe'

Global Const $tagICONRESDIR = 'byte Width;byte Height;byte ColorCount;byte Reserved;ushort Planes;ushort BitCount;dword BytesInRes;ushort IconId;'
Global Const $tagNEWHEADER = 'ushort Reserved;ushort ResType;ushort ResCount;' ; & $tagICONRESDIR[ResCount]

; Select icon to update resource
Local $sIcon = FileOpenDialog('Select File', @ScriptDir & '\Extras', 'Icon Files (*.ico)', BitOR($FD_FILEMUSTEXIST, $FD_PATHMUSTEXIST), 'Script.ico')
If Not $sIcon Then
        Exit
EndIf

; Create simple executable file (MyProg.exe) in which will be added icon
If Not FileCopy(@ScriptDir & '\Extras\MyProg.exe', $g_sExe, $FC_OVERWRITE) Then
        If MsgBox(($MB_OKCANCEL + $MB_ICONERROR + $MB_SYSTEMMODAL), 'Error', 'Unable to copy MyProg.exe or file already exist in the current directory.') <> 1 Then
                Exit
        EndIf
        FileCopy(@ScriptDir & '\Extras\MyProg.exe', $g_sExe, $FC_OVERWRITE)
EndIf

Local $iError = 1
Do
        ; Begin update resources
        Local $hUpdate = _WinAPI_BeginUpdateResource($g_sExe)
        If @error Then
                ExitLoop
        EndIf
        ; Read .ico file as raw binary data into the structure
        Local $tIcon = DllStructCreate('ushort Reserved;ushort Type;ushort Count;byte[' & (FileGetSize($sIcon) - 6) & ']')
        Local $hFile = _WinAPI_CreateFile($sIcon, 2, 2)
        If Not $hFile Then
                ExitLoop
        EndIf
        Local $iBytes = 0
        _WinAPI_ReadFile($hFile, $tIcon, DllStructGetSize($tIcon), $iBytes)
        _WinAPI_CloseHandle($hFile)
        If Not $iBytes Then
                ExitLoop
        EndIf
        ; Add all icons from .ico file into the RT_ICON resources identified as 400, 401, etc., and fill group icons structure
        Local $iCount = DllStructGetData($tIcon, 'Count')
        Local $tDir = DllStructCreate($tagNEWHEADER & 'byte[' & (14 * $iCount) & ']')
        Local $pDir = DllStructGetPtr($tDir)
        DllStructSetData($tDir, 'Reserved', 0)
        DllStructSetData($tDir, 'ResType', 1)
        DllStructSetData($tDir, 'ResCount', $iCount)
        Local $tInfo, $iSize, $tData, $iID = 400
        Local $pIcon = DllStructGetPtr($tIcon)
        For $i = 1 To $iCount
                $tInfo = DllStructCreate('byte Width;byte Heigth;byte Colors;byte Reserved;ushort Planes;ushort BPP;dword Size;dword Offset', $pIcon + 6 + 16 * ($i - 1))
                $iSize = DllStructGetData($tInfo, 'Size')
                If Not _WinAPI_UpdateResource($hUpdate, $RT_ICON, $iID, 0, $pIcon + DllStructGetData($tInfo, 'Offset'), $iSize) Then
                        ExitLoop 2
                EndIf
                $tData = DllStructCreate($tagICONRESDIR, $pDir + 6 + 14 * ($i - 1))
                DllStructSetData($tData, 'Width', DllStructGetData($tInfo, 'Width'))
                DllStructSetData($tData, 'Height', DllStructGetData($tInfo, 'Heigth'))
                DllStructSetData($tData, 'ColorCount', DllStructGetData($tInfo, 'Colors'))
                DllStructSetData($tData, 'Reserved', 0)
                DllStructSetData($tData, 'Planes', DllStructGetData($tInfo, 'Planes'))
                DllStructSetData($tData, 'BitCount', DllStructGetData($tInfo, 'BPP'))
                DllStructSetData($tData, 'BytesInRes', $iSize)
                DllStructSetData($tData, 'IconId', $iID)
                $iID += 1
        Next
        ; Add new RT_GROUP_ICON resource named as "MAINICON"
        If Not _WinAPI_UpdateResource($hUpdate, $RT_GROUP_ICON, 'MAINICON', 0, $pDir, DllStructGetSize($tDir)) Then
                ExitLoop
        EndIf
        $iError = 0
Until 1

; Save or discard changes of the resources within an executable file
If Not _WinAPI_EndUpdateResource($hUpdate, $iError) Then
        $iError = 1
EndIf

; Show message if an error occurred
If $iError Then
        MsgBox(($MB_ICONERROR + $MB_SYSTEMMODAL), 'Error', 'Unable to change resources.')
EndIf