Sorry if this sounds stupid, but what do you mean by "the hairstyles are probably in a similar system to that of the Witcher 2"? You mean hairstyles could be changed in The Witcher 2? Or that they are in a similar style (haircut or hairdo... don't know the exact word :P)?
And another question: is it possible to change hairstyle in-game? Or do I have to always check and uncheck the DLC from the configure button?
What I meant answers both of your questions.
Yes, you can change your hair styles ingame. The DLC just added more of them (or the option itself I am not 100% sure).
By saying the system is similar to the one we saw in the Witcher 2 I meant that like in the previous game you will need to go and see a person (a Barber) to have him cut your hair and beard.
Hope I helped
Quick update as I managed to fix my issue.
I thought about trying to verify the game files but that option was greyed out. I searched around found out that it's supposed to be available. So the solution to this one was to force Galaxy to recheck the files.
I made a backup of the game. Uninstalled it and then moved the backup back into place. Then told Galaxy to download the game and it started to compare the files to my local files. It then proceeded to download ~15mb and it was done.
I can now see all the DLC and I can verify the game files at will.
If you don't mind I will add your problem and solution to the main post.