Others will know more about this than myself, but perfumes for hair are quite an old concept. There are not many of the classic Guerlain perfumes that have not been released in this form ('perfume pour les cheveux'), especially ubiquitous being Shalimar. I have no idea about the difference in composition.
On a side note - I use Eau du Coq as my hair conditioner with good results. The oils in it leaves my hair hydrated. and with little chemical residue.