The escaping required should be pretty minimal. You only need to escape the $
and the parentheses like so
<search regex="true" position="replace"><![CDATA[~\$this->load->model\(.*?\);~]]></search>
Also as you've rightly done in your answer to this, you need to add a delimiter (I find ~
is far less likely to be in a string than /
hence using that instead)