Thanks y'all. That answers my question: it's not threaded, it's the same as the headset cups. Wanted to know before I mangled it trying the wrong way.Think I'll take it in to our machine shop at work and see if there's something that can help me get it off. If nothing looks like it'd work, I might just mask it. Or I could stop by a bike shop.
Getting it back on should be okay. We have many sizes of pipe scraps that should work. That's how I got the headset cups off.