Because you already have the melanurus wrasse, I would be hesitant as I have had mixed experiences with melanurus wrasses. The first male I had was lovely, got along with everyone, was fine with new additions, and never went after clean up crew. He survived my beginner mistakes and lived for many years.
My second one was a nightmare and actually killed my barred hamlet (still upset... haven't been able to find a barred hamlet since). He took out nearly all of my cleanup crew too before I finally got him out of the tank. New additions would have been impossible with him.
Since your melanurus is not fully mature, you may be OK, but if you want to try it, I would do it sooner rather than later. I wouldn't try it personally but fully admit to being risk averse when it comes to stocking list. The few times I have tried to push boundaries I did not succeed.