Can I customize the IP Restrictions template file? I am playing with the IP address restrictions system,which seems to work well. Is there any way for me to customize the template? Can I redirect to a WP page so that the customer will see something pretty?

Yes. Please make a copy of this file:

/s2member/includes/templates/errors/ip-restrictions.php

See also: source code on GitHub

and place it into a new file of your own here:

/wp-content/ip-restrictions.php

Now you can customize /wp-content/ip-restrictions.php in whatever way you like.

You can use PHP, WordPress, and s2Member functionality in this template file; i.e., <?php ?> tags can be used in this template if you need them.

See also: Hacking s2Member® Plugin w/ Hooks/Filters for WordPress