Yeah, you have to copy and paste the contents of your dosearch.php file, and put it in there. Then, you modify that file ....
I explained it in the instructions, but may have not been clear.
Should I explain more?
(Basically, you create dosearchlatest.php by modifying dosearch.php, but dosearch.php is left intact and original, so technically you're adding files and really only touch the ubbt code by changing the registerednav template.)
-peter