I'm the OP on this. Here's the current setup on this key switch:
Yes. I guess I assumed (hoped) that the swtich was designed such that if it was removed, the wires would break away in some fashion that would leave them inaccessible from the front. At least, that's what I would have done. But of course I won't know until I remove it.
So there must be a part B that's the receiver. This is a Sears opener from 1972, and the mechanical box still works fine, but the original transmitters and receiver died long ago, and instead I use this set:
I see that there is also a 318K available, a keypad which appears to use the same receiver. If so, that would be pretty straightforward. However, not having seen the 318K, it's not clear how secure it is. Does it simply transmit whatever you enter to the receiver, or do you set a specific code in the keypad? I know that both the T and R of the current setup have to have the dipswitches set the same way. Well, I'll need to look into that. It seems a lot of things that should be secure really aren't, starting with padlocks.
But I guess the basic question is whether I'd rather use a key or a keypad. It's basically for times when I need to give someone who doesn't have a clicker access to the house when I'm not there. And if secure, it seems the keypad is more convenient, and if it's done correctly, more secure. I assume all current construction uses keypads.