Really, this is a profound question! We are not to mix things together that God did not make to go together, it is something God says to do in spirit and truth---to do literally but only as we do it spiritually. God looks at our heart.
If you look at it in it's deepest sense, it would be how we look at law. Is it something like the law the police go by where you either obey or you go to jail, or is it more as the word Torah says---is it guidance to a good life. Scripture seems to indicate we can obey to the letter giving all sorts of rules around the spiritual law and obey all those without once obeying the spirit of the law.
I am watching two households who make it a law not to have TV in their homes. One pair of frowning parents forbids TV, saying it makes them holy sort of things. The other household doesn't have TV to excite the children, take away their time from bonding and fun things, and to live closer to the Lord. Neither has TV for their children, but what a difference in the children.
It is the same with mixing real and fake hair!