i don't use notepad++ so can't verify, but i guess you'd want something like this:
Code:
find:
(<p class="someclass">)(<a href="[^"]+")(.*?)(</div>)
replace:
\1\2\3\1\2>Go Back</a></p>\4
there's probably an option to turn on 'dot matches new line' in the search/replace field which you should use. might have to play around with it to get it working properly but hope it's helpful