LuCI is based on MVC (Model–view–controller). The '/usr/lib/lua/luci/controller/arduino/index.lua' is the controller file and byte compile.
Linino/Openwrt/LuCI are all open source, and you could easily replace it with source file.
opkg update
opkg install wget
cd /usr/lib/lua/luci/controller/arduino/
mv index.lua index.lua.bk
wget https://raw.githubusercontent.com/arduino/YunWebUI/master/usr/lib/lua/luci/controller/arduino/index.lua --no-check-certificate
/etc/init.d/uhttpd restart