[KaktoR]

Try like this

  if LowResourceCB.Checked then begin
    ExtractTemporaryFile('low_ARC.ini');
    ExtractTemporaryFile('low_CLS.ini');
    RenameFile(ExpandConstant('{tmp}\low_ARC.ini', '{tmp}\Arc.ini'));
    RenameFile(ExpandConstant('{tmp}\low_CLS.ini', '{tmp}\Cls.ini'));
  end else begin
    ExtractTemporaryFile('ARC.INI');
    ExtractTemporaryFile('CLS.INI');
  end;

This code has to be placed BEFORE archive unpacking begins.