I couldn’t figure out how to do it using the template, but I was able to do it using css. To add “By” before the author:
Add this to the main css file:
.lcp_byline:before {
content: "By: ";
}
Add this to the shortcode:
author=yes author_tag=span author_class=lcp_byline
Result:
By: Author Name
Hope this helps!