var Stream : TStream;

UOCFGStringList := TStringList.Create;
try
  Stream := nil;
  if FileExists(ClientDir + 'uo.cfg') then
    try
      Stream := TFileStream.Create(ClientDir + 'uo.cfg', fmShareDenyNone);
      UOCFGStringList.LoadFromStream(Stream);
    finally
      if Assigned(Stream) then Stream.DisposeOf;
    end;
  i := 0;
  while i < UOCFGStringList.Count do
  begin
    if UOCFGStringList.Strings[i].Contains('AcctID') then
      UOCFGStringList.Delete(i);
    if i >= UOCFGStringList.Count then Break;
    if UOCFGStringList.Strings[i].Contains('AcctPassword') then
      UOCFGStringList.Delete(i);
    if i >= UOCFGStringList.Count then Break;
    //...еще пять таких же
    Inc(i);
  end;

  UOCFGStringList.Add('AcctPassword=' + String(b));
  UOCFGStringList.Add('RememberAcctPW=on');

  try
    try
      if FileExists(ClientDir + 'uo.cfg') then
        Stream := TFileStream.Create(ClientDir + 'uo.cfg',
          fmOpenWrite + fmShareDenyNone)
      else
        Stream := TFileStream.Create(ClientDir + 'uo.cfg',
          fmCreate);
    except
      //обрабатываю ошибку
      Exit;
    end;
    UOCFGStringList.SaveToStream(Stream);
  finally
    if  Assigned(Stream) then Stream.DisposeOf;
  end;
finally
  UOCFGStringList.Free;
end;