I tried merging that, as well - but the Mosin was replacing another Rifle in the P90s Icon File, which I didn't care much about since it was an ugly one either Way.
I merged the Textfiles together manually with Notepad++ Compare Feature but the Inventory Icons File was the real Problem. My only Problem was, both change the same Files, of course.
I'm new to the whole Franchise and tried to install the FN-P90 and Mosin from Gosuke.