Sure, apart from one is a $20 watch and an insignificant investment of time and energy versus a lot of expensive, risky hoops with a high-level of skill to pull off. People always lean on this analogy of cars, but frequently there's no analogy required. The watch mod isn't for you and that's fine.
Thanks for the condensation. It's just a philosophical comment along the lines of the Ship of Theseus, can it still be called the F91W if you replace a major component? Especially saying "Ah yeah the F91W can run custom software, just gut it out add a component to run that software!".
If you swap out the CPU on your computer, is your computer still the same computer? Something has changed. Perhaps a more accurate way of looking at a model name like an F91W is that it's a configuration of components. Ergo, an "F91W configuration can be modified to do xyz". Is it based off of an F91W? Yup. The information that's being conveyed is that if you own a cheap F91W, for a few bucks in parts and a little time, you can do something interesting with it.