As we can not trim or alter our eyebrows, what about the hair in between (unibrow)?
Is it permissible to thread the hair that is between our eyebrows? (For men)
According to the ruling of Grand Ayatollah Khamenei as a Shia Marja' al Taqlid:
Shaving (thread) and decoration is not considered as a haram act by itself, but it would be haram if it is counted as the cause of concupiscence stimulation or the man makes himself as a women.
Therefore in accordance with the mentioned ruling we can say that perhaps it could be considered as a haram act, since it could make them relatively or even completely similar to women…
Yes, you may, except if you are afraid of Mazhab-Fanatics, for they will accuse you of this haram doing. That trimming has been indoctrinated by certain scholars as haram because it changes the creation of Allah. According to this view, woman and man are both forbidden from trimming them.
But, for certain people Allah has made them uneasy with too much hair so, it is a case of darurah (necessity) for you to trim your hair (on any part of your body, face, head etc.).
As far as women are concerned, scholars have come to a common viewpoint that it's allowed if it's for beautification. Hope this helps.