I do know that for fact. I have at least 3 personal friends who are mechanics, one in a dealership, and two who own private shops. They think I am nuts for waisting my time doing bleeding when I need to change a caliper.
Yep boiling would make the pedal go down. It also would make the fluid flow when you disconnect the pipe. Fluid running out the pipe would be a good thing. That way no air getting in. If then attached to a fully filled caliper not much air if any would get in. As long as the reservoir didn’t get too low.
Of course, we all know private shops and dealers would
never take shortcuts on jobs they do all the time, right? If someone opened up my brake system and didn't bleed afterwards I would never use that shop again; just because you can get away with it 999 times out of a thousand doesn't mean it's the proper procedure (and the plaintiff's lawyer in a lawsuit would bring it up if there was an accident involving the brakes, and you wouldn't want me on the jury).
How often do you swap out calipers? I've had mine off once in 35years/145K miles for rebuild--that I can recall, at least--but I've had to replace several clutch and brake cylinders. The job just isn't done that often, you've got the car up on jackstands or a lift with the wheels off, why wouldn't you take 20 minutes to bleed/flush the system while you're at it? All the shop manuals I've read, for several makes, specify a complete fluid flush every 2-3 years. That may be overkill but you can't say it's a bad idea; DoT 3&4 are hygroscopic--they absorb atmospheric moisture readily (read the label on the bottle)--and DoT 5 causes moisture to pool in the low spots. Suspension and brakes are no place to half-ass a job; if the engine doesn't start you don't go, but if the brakes fail you don't stop.
In the movies or on the track, you might get away with a somewhat softer pedal for a few miles; it's a calculated risk. Not worth it on a 'family' car.