Yopu could copy the trusted_tel_login_cart() function (line 844 to line 1052 in extras.php) into your child theme functions.php file, and change the part where the ‘Register’ link is found.
On line 946 change this part:
<a href="<?php echo $woo_account_page_url;?>"><?php echo $woo_account_reg_title;?></a>
to something like this:
<a href="http://www.mywebsite.com/my-registration-page/"></a>
PS to write code into a forum post, switch from Visual tab to Text tab and you can wrap the code with code tags using the ‘code’ button.