If you know how to re-wire stuff properly, it's conceptually an easy process (some devices can be tricky to take apart).
For example, on that toaster you can replace the cable with a longer one, put a new plug on it if that gets worn out, or if absolutely needed splice the cable with another one (that's for when the device can't be opened up for some reason)
Unplug toaster before cutting the power cord, or any other maintenance, such as cleaning the 3 years of crumb its collected.
The most preferred method is to replace the entire cable, the wires connect inside the device somewhere, probably with simple screw terminals. Replace the whole cable and you don't have to worry about any weak points in the splice or insulation, because there are none.
The danger is when you don't know how electricity and wiring works or get lazy and take shortcuts.
There's a bunch that can go wrong, some of them have potentially life ending consequences, which is why it's a bad idea to work on electronics...unless you take the time to learn how they work and be smart about it.
For a cheap toaster, yes, I wouldn't bother either unless it was the best toaster ever. But for more expensive things, like an air fryer, power tools, vacuums, any thing with sentimental value... it is a great skill to learn how to do safely.
Just replacing a broken plug on an extension cord can save you big, the good cords are going for $20+, a new plug is closer to $2 (although replacing the plug removes its safety for outdoor use as it's no longer a water tight seal).
Its usually cheaper to replace the damaged part than the whole unit.
Have no idea about those standards to be honest, all sorts of Chinese shit appliances get imported here, I don't think we have a code that regulates that.
Yeah I know plenty of chenese stuff ignores it. I forget where it's said but countertop appliances are supposed to be 3' cords and others are supposed to have 6' cords. And then in houses you're supposed to have plugs at those distances so people usually shouldn't need extension cords.