Modifying php files for co-author

Co-Author looks like what I need, but I’m having trouble with the whole modify-the-PHP files thing for the theme (SimpleMag) I’m using. This seems to be the byline code in SimpleMag:

<?php if( $ti_option['site_author_name'] == 1 ) { ?>
                <span class="entry-author">
                    <?php _e( 'By','themetext' ); ?> <a href="<?php echo get_author_posts_url( get_the_author_meta( 'ID' ) ); ?>" rel="author"><?php the_author_meta( 'display_name' ); ?></a>
                </span>
                <?php } ?>

Is it as simple as using the “if” part of the co-author code and making the above the “else”? Or is it more complicated than that?

http://ww.wp.xz.cn/plugins/co-authors-plus/