Install:

Install the folder to "mods/update/x64/dlcpacks/" with OpenIV.
Go to "mods/update/update.rpf/common/data/" and edit DLCLIST.XML file, adding a new line for the new Add-On.

How to use it:
Now, you can drag & drop texture (ytf and ytd files) and YMAP files into "textures.rpf" file of your Add-On. They'll be loaded
automatically by the game when started. This way you don't need to copy "x64.rpf" files to your "mods" folder to replace textures,
saving a lot of GB :)

Enjoy!