Wow that is an expensive diode. You don't need a fast switching one.I would say yes a diode drop in the USB line is going to give you trouble some where down the line.The point is that you are trying to protect your Mac from something you don't know, and it looks like we will never find out. Therefore it is impossible to give any measures that will protect it.I have used a MacBook pro for over 5 years on many different makes of arduino and have not encountered any problem. And I think that goes for every other member on this forum. So I would advise against doing this modification to your cable.