Inno Setup ChangeEnvironment not working

I am using InnoSetup to create an installer but the Environment is not refreshed after the installation. The user has to restart the computer in order for the Environmental Variable to be refreshed.

This is my code any help will be appreciated.

    [Setup]
ChangesEnvironment = yes
AppName=ffmpeg
AppId=ffmpeg
AppVerName=ffmpeg
DefaultDirName={pf}ffmpeg
DefaultGroupName=ffmpeg

SourceDir=c:/Users/pkallonis/Desktop/ffmpeg_installer/ffmpeg
OutputDir=c:/Users/pkallonis/Desktop/ffmpeg_installer
OutputBaseFilename = ffmpeg-win32-setup

DisableProgramGroupPage = yes
Compression=lzma
SolidCompression=yes


[Files]
Source: "*.*"; DestDir: "{app}";

; the code below is to append to the path and remove on uninstalling
; to put off, comment the two functions at the end

[Code]
function Replace(Dest, SubStr, Str: string): string;
var
  Position: Integer;
  Ok: Integer;
begin
  Ok := 1;
  while Ok > 0 do
  begin
    Position:=Pos(SubStr, Dest);
    if Position > 0 then
    begin
      Delete(Dest, Position, Length(SubStr));
      Insert(Str, Dest, Position);
    end else
      Ok := 0;
  end
  Result:=Dest;
end;

procedure AppendToPath();
var
  V: string;
  Str: string;
begin
  RegQueryStringValue(HKLM, 'SYSTEMCurrentControlSetControlSession ManagerEnvironment', 'Path', V)
  Str := ExpandConstant('{app}');
  V := Replace(V, Str, '');
  V := V + ';' + Str;
  V := Replace(V,';;',';');
  RegWriteStringValue(HKLM, 'SYSTEMCurrentControlSetControlSession ManagerEnvironment', 'Path', V)

 // MsgBox(V, mbInformation, MB_OK); 
end;

procedure RemoveFromPath();
var
  V: string;
  Str: string;
begin
  RegQueryStringValue(HKLM, 'SYSTEMCurrentControlSetControlSession ManagerEnvironment', 'Path', V)
  Str := ExpandConstant('{app}');
  V := Replace(V, Str, '');
  V := Replace(V,';;',';');
  RegWriteStringValue(HKLM, 'SYSTEMCurrentControlSetControlSession ManagerEnvironment', 'Path', V)
  //MsgBox(V, mbInformation, MB_OK);
end;

procedure DeinitializeSetup();
begin
  AppendToPath();
end;

procedure DeinitializeUninstall();
begin
  RemoveFromPath();
end;