With small changes such as this, the easiest way is to use the new config, and re-apply your own changes;
/etc/lighttpd/lighttpd.conf-opkg /etc/lighttpd/lighttpd.conf
The important change here is the three include lines at the bottom.
As a side note, please use code blocks when posting code (or large amount of text), such as the diff. Edit your post, and enclose it in tripple backtics (```) for a code block, such as the one in my post.
We should probably also continue this discussion in Lighttpd not starting anymore, to avoid cluttering this one