just copy the original file /html/portlet/login/create_account_user_name.jspf inside your docroot/custom_jsp/html/portlet/login/ directory. Despite what eclipse shows to you, any jsp/jspf of your hook will replace the original liferay file.
I successfully edited file /html/portlet/users_admin/user/details_user_name.jspf (i disabled field modifications for users coming from ldap).
Please note that in liferay-hook.xml the only directive you can set for jsp overriding is
<custom-jsp-dir>/custom_jsp</custom-jsp-dir>
You wont need to specify all jsp files, just your root directory