Copying files;; pretty simple go to your $PCSX2_CONFIG and copy the the textures folder from this directory to your PCSX2 CONFIG
$PCSX2_CONFIG depends on your Opreating system.
Note For mac : You cant acess it directly from finder, you have to go and "Search it" For Mac it is Library/Application Support/PCSX2/(This is where the textures go)
Enabling MODS Since we cannot use JSGME, We have to copy these files manually;; It's really easy
To enable copy the MOD from the MODS/THE_MOD_YOU_WANT/textures/SLUS-20919/replacements/zall to $PCSX2_CONFIG textures/SLUS-20919/replacements/zall/
So for Controller_Xbox_Buttons (Atleast on Arch Linux)
I go into $THIS_DIR (The directory your reading this file from)
Make sure you already have copied the textures into $PCSX2_CONFIG (For me this is .config/PCSX2)
Then i go into MODS/Controller_Xbox_Buttons/textures/SLUS-20919/replacements/zall/
Copy all the files from this directory (Should be a bunch of pngs, then copy them to you $PCSX2_CONFIG/textures/SLUS-20919/replacements/zall and overwrite the PS2 Buttons.
Hope you get the key concepts of Texture replacement in PCSX2, and atleast now you can show some knowledge and do this by yourself.