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 [code=plaintext];[Registry]
;Root: "HKCU"; Subkey: "Software\Microsoft\Office\14.0\Excel\Options"; ValueType: string; ValueName: "OPEN1"; ValueData: "C:\Users\UserName\AppData\Roaming\Microsoft\AddIns\AddIn.xlam"; Flags: createvalueifdoesntexist uninsdeletevalue

[code]
procedure CurStepChanged(CurStep: TSetupStep);
var
  ValueExists: Boolean;
  AddInCount: Integer;
  ValueName: String;
  SubKey: String;
  Data: String;
begin
  if (CurStep = ssInstall) then
  begin
    ValueExists := false;
    AddInCount := 0;
    SubKey := 'Software\Microsoft\Office\14.0\Excel\Options';
    ValueName := 'OPEN';
    Data := 'C:\Users\' + GetUserNameString() + '\AppData\Roaming\Microsoft\AddIns\AddIn.xlam';
    repeat
      if (not RegValueExists(HKEY_CURRENT_USER, SubKey, ValueName)) then
      begin
        RegWriteStringValue(HKEY_CURRENT_USER, SubKey, ValueName, Data);
        ValueExists := true;
      end
      else
      begin
        AddInCount := AddInCount + 1;
        ValueName := ValueName + IntToStr(AddInCount);
      end;
    until ValueExists;
  end;
end;