Verdict: I was right the first time, when I was working on fixing the rear tire. You can't take that chain off without breaking it.
The problem is, the chain passes through the swingarm. Tracing its path, I saw that it forms a loop around the swingarm shaft inside the frame. If you make the "OK" hand sign with both hands, and pass one loop through the other at 90°, that's approximately the configuration.
So there's no way to get the chain off without either breaking the chain, or removing the swingarm. *sigh*
Even better? You can't use a conventional "clip-style" master link in the damn thing. You've got to use a press-fit riveted type master link. Argh etc.
So at the minimum I need a $20 tool plus the correct master links, which aren't reusable.
...I honestly don't understand what the advantage is to the "endless" type chain. I'm seeing that the clip-type master link chains have a minimum tensile strength of 6,600 lbs, and some are even greater than that; is the endless chain stronger? Does it need to be, on a 2-cylinder 450 cc bike?
On the plus side, a quick Ebay search shows me I don't have to pay any $150 for a new chain as there are several for sale there--some starting at $25.
Or I could get a blue chain for $70. Whee!
And it's a #530 chain, so I know what size master link to buy, anyway. I suppose I could ask the guys at the Yamaha shop. "Say, do I really need to--?"
Regardless of what I do, it seems like all the parts I need for this thing cost $20-$25. Rear brake shoes? $21. Chain? $25. Front brake pads? $20. The rear wheel bearings turn fine but one makes a little bit of noise; a set of bearings and dust seals is $25. And I bet I could tap them in and out with tools I have on hand. ...it's a bit more than "nickle and dime" but it's not egregious the way some things are.
But the first thing I want to attend to is that chain, dang it. It's better than it was after I cleaned and lubed it, but it's not right, and I want it to be right.