[peterf1999]

installer doesnt skip if regkey exists - always run

function InitializeSetup(): Boolean;

var
ResultCode: integer;

begin

if not RegKeyExists(HKEY_LOCAL_MACHINE, 'Software\Microsoft\Windows\CurrentVersion\Uninstall\{81FF29CE-2D23-45FC-8BDE-7491A15F2B02}') then

   begin

     Exec (ExpandConstant('{src}\setup.exe'),'', '', SW_SHOW,
     ewWaitUntilTerminated, ResultCode)
     Result:=TRUE
     
   end else

       begin
       
        Exec (ExpandConstant('{src}\setup.exe'),'', '', SW_SHOW,
        ewWaitUntilTerminated, ResultCode)
// return false and abort inno setup, original setup.exe launched and it asks
// if u want to remove the game
       end;

InitializeSetup event does it :P

installer dont run nv_arc.exe if regkey exists :)

procedure CurStepChanged does it
look carefully the code

it's not a joke, i tested it and works 100%