Not really sure what the question is here, but the answer is that letters of recommendation are mandatory to submit (I forget the minimum #), and will contribute to the assessment of your potential to be appointed. I would recommend including the extra LOR if possible, but make sure it is well written and adds value/perspective to the mandatory letters. There is no way to know if simply having more LORs adds to your score, but it is reasonable to expect that an extra well-written letter will give admissions a better idea of who you are and subsequently improve your score.
The flip side: if you submit an extra LOR that is poorly written, poorly formatted, and adds little value to the information already presented in the minimum LORs, there is a good chance it will hurt you.