well yes and no, the problem with this is that we are not the server, unlike other source games like garry's mod or CS, it will not have people load your files into there cache, so instead of them seeing a cannon or something it would run normally to them, its much like the nude mod, you apply it and you can see other chars naked and yourself but to them you are in your underwear.
as for their being left over cannon's and such, no there are scripts that look like it, i was once looking through the HFS files and found a working ballista with damage rate and speed, as for having it spawn in game, is another story it would require a DEV console.