how to modify content.php in child theme

I want to modify the wording for the Leave a comment section of content.php.
What I have done is to copy all of content.php to the child theme and change the one line I need to:
<?php comments_popup_link( '<span class="leave-reply">' . __( 'Lets kick it off, leave a comment', 'twentytwelve' ) . '</span>', __( 'Only 1 comment. What are your thoughts?', 'twentytwelve' ), __( '% Comments, leave your thoughts', 'twentytwelve' ) ); ?>

Is there a better way to make this change? One that does not require copying all of content.php to the child theme.

Thanks
Vincent