Creating a custom patch for a different package

I have a custom package that uses package/feeds/packages/openvpn functionality and i want to create a patch in my custom package that patches openvpn init.d script.

I have read about patches on openwrt site but I cannot find the openvpn init.d script to patch in build_dir.

I am using the official default openwrt build from github and I havent modified any default packages.

please keep only one post for one same subject !