Reverse engineering doesn't help for iOS very much since even if you build your own version of their app with that feature unlocked, iOS doesn't allow you to sideload.

You'd have to pay $100/year for an apple developer account and then refresh the app every 14 days (since publishing your own hacked version on the appstore would plainly be a copyright and trademark violation, and if you use a developer account to load a developer version of an app on your device, you have to constantly refresh it).

Switch to one of the linux phones if you actually want to install software on your device.

What's the point of that, when the body fat % measurement is highly inaccurate on these?

reverse engineering to get the garbage out from sensors/.