Index: src/wp-includes/ms-functions.php
===================================================================
--- src/wp-includes/ms-functions.php	(revision 36711)
+++ src/wp-includes/ms-functions.php	(working copy)
@@ -1457,6 +1457,22 @@
 	$url = get_blogaddress_by_id($blog_id);
 	$user = get_userdata( $user_id );
 
+	/**
+	 * Filter the content of the welcome email after site activation before tokenized replacements have been made.
+	 *
+	 * Content should be formatted for transmission via wp_mail().
+	 *
+	 * @since x.x.x
+	 *
+	 * @param string $welcome_email Message body of the email.
+	 * @param int    $blog_id       Blog ID.
+	 * @param int    $user_id       User ID.
+	 * @param string $password      User password.
+	 * @param string $title         Site title.
+	 * @param array  $meta          Signup meta data.
+	 */
+	$welcome_email = apply_filters( 'tokenized_update_welcome_email', $welcome_email, $blog_id, $user_id, $password, $title, $meta );
+
 	$welcome_email = str_replace( 'SITE_NAME', $current_site->site_name, $welcome_email );
 	$welcome_email = str_replace( 'BLOG_TITLE', $title, $welcome_email );
 	$welcome_email = str_replace( 'BLOG_URL', $url, $welcome_email );