I would first do your best to keep your rude neighbor as far away from your pond as possible. It is hard to manage a pond when you don't know what's coming out of it!

If you stocked 100 F1 bass into a quarter acre pond, you probably stocked at least twice if not 4 times the number you should have if your goal is to grow large bass... I wouldn't recommend adding anymore bass. A quarter acre pond at best can maybe hold 30 pounds of bass and if fertilized you may be able to squeeze 40 pounds but that's pushing it... Manage the fish you still have properly and I think you can grow a few nice bass.

As far as introducing wild shellcrackers(RES) form Guntersville, you run the risk of introducing an unwanted parasite or disease. You can add them, but know that is a risk... Tilapia may help with the FA problem and would be great forage for your bass. A 1/4 acre pond is tough to work with when it comes to growing trophy bass, especially when you have a neighbor with sticky fingers. However, manage it the right way and you can grow a few nice sized bass...

Fertilization may help with the carrying capacity of your pond as would aeration so you may want to strongly look into both. I wouldn't add anymore bass, and be cognizant of the risks you run when introducing wild fish to your pond. Break out the land mines and trip wires and you'll be set!