First you need MH2 TEX Editor and MH2 MDL Editor 
Insert the textures and model in the level
Decompress the resource3 glg with the mdl editor and edit it with Notepad++ or js notepad and change the model name used for the razor to "KNIFE_(CT)"
And then ur done with that 

How to add the icon
Use the TEX Editor to open the ingame.tex file in global/pictures and replace the razor one with the icon.tga