Can Section access be restricted at Entry Type level?
When you mention new user group, is that a new group of admins/back end users or just people browsing on the front end?

If it's on the front end, just checking the logged in user's group in twig against a new restricted entry type could give you want you want.

{% if entry.type == "restrictedEntryType" and currentUser and currentUser.isInGroup('newUserGroup') %}

   {# let them through #}
   {% include "whatever/restricted_content.html" %}

{% else %}
   &lt;p&gt;Thou shall not pass! You need to log in to see this content.&lt;/p&gt;
{%endif%}


If it's the back end, like you said, you'd have to do a serious refactor to manage it properly. Put all the restricted content in one structure and only give access to admins/users you want to have edit the content.  You may end up doing that anyway just to keep everything sane, depending on how siphoned off your content is.

To move a structure from one section to another, check out Brandon Kelly's canonical answer.