I hope the criminal court would have something to say about caltrops used that way, even in the US. While you are at it, why not just rig a claymore mine on the boat. "Front toward enemy" seem to be a concept you understand and like.

If someone want to convert a H-18 into a semi-F18 after due warning, why not? Comparing the respective performance of the platforms afterwards will be a learning experience that will further the understanding of the F-18 platform.
I think this project looks like fun, even if the result will not be an F-18. Anyone with the initiative and will to go trough with projects like this have my admiration. Is it a smart thing to do? Well, that certainly depends on what is expected from the results. Not everybody are full time racers.