This mod replaces hats and the helmet worn by Niko, with a flat cap, in the look of Peaky Blinders.
+as a bonus- I have replaced Roman's helmet with the same flat cap. You can only see it when you get him on a bike tho.
The hats model is taken from one of in-game peds, with me only remaking few textures and converting it for Niko,

The cap has 3 textures- gray, dark blue and black. I have replaced the helmet also with the gray cap also.

!!!The model of Niko seen in my screenshots is not included!!!
If you are interested- I am using a Jason Statham face texture made by timothyR: https://www.gtainside.com/en/gta4/skins/29755-jason-statham-mod/

and Niko Bellic New Suit Pack By MikaelCao:
https://www.gtainside.com/en/gta4/skins/88341-niko-bellic-new-suit-pack-v2

To install the mod- you must replace the pedprops.img in \GTAIV\pc\models\cdimages\

Enjoy