Yes, I had the rubber freeze plug installed with a jam nut against the included one and blue loctite into the plastic pipe. I put the hose AND symposer back over it for stock look. However, I removed the actual symposer later, when I installed the ramair silicone intake hose and whoosh crossover pipe. Then I removed the freeze plug and put in a used boomba w/threaded hole I bought used here.
If you remove the symposer, but keep the rubber hose on, you can put the freeze plug in that. See the thread he posted above.