This tool replaces textures in .Arc files for MHGU. It scans each arc in the target directory and replaces any textures with the same name. It can look though the entire NativeNX folder if the exact location of your replacement is not known or there are multiple replacements to be done.
A version of the installer with the runtime componets is located here https://www.mediafire.com/file/sx0r97tcgegrvgm/MHGU_Tex_Tool_Runtime.zip/file. If you installed my Charm Exporter you probably already have them.
A readme is included in the data folder that explains how to use the tool.
I am trying something different with my compiling method so your OS may be unhappy about a digital certificate or maybe something else. It works fine on mine of course but that doesn't matter much for you. Make an issue if you'd like, should that occur. I'll try to take less then a year to fix it.
I already have some thoughts on making this faster and might upgrade it later.