I don't use subforums now, so I cannot check if it still works, but I disabled the existing template modification and made a new one.
Template: forum_view
Modification Key: blah
Description: blah blah
Search type: Simple replacement
Find:
<xf:extension id="above_thread_list"></xf:extension>
Replace:
<xf:include template="ozzmodzForumPrefix_block"/>
$0
That worked for me.
Alternatively, place <xf:include template="ozzmodzForumPrefix_block"/> in the forum_view template and use conditions but that way you would probably need to wrap the existing template modification in conditions too.