The NCAA rules don't specify exact placement of the hurdles because the actual lap distance can vary quite a bit depending on the water jump location.
The rules specify that the distance from the starting point to the finish line on the first lap shall not include any hurdles and that there be at least 68 meters between the last hurdle and the finish line. Beyond that, they suggest 78 meters between hurdles but allow for variations due to water jump locations. They also define the staring point for a lap and say that the water jump must be the fourth hurdle in each full lap.
In short, the rules don't say you can't place an extra hurdle in at the end but that would not be in the spirit of the rules. The way I interpret the rules, if you did so, it could only be placed between the final water jump and the last hurdle on the straightaway.