Any video apk you install can't consume more than what the kernel allows for. It can't change throttling parameters, cant change apu speed, and it can't change how fast the battery can be charged or the upper limit it will charge to. All apks can only do what they're allowed to do, and it's a lot less than what flashed phones and custom kernels can do. Right now, for instance, your phones battery never actually charges to max capacity, or discharges to minimum capacity before powering down. Your "100%" is actually more like 90%, but it increases the batts lifespan because the most damage done to lithium batteries is at the high end and low end of what it can hold. Same for all the fast charge stuff. Fast charging is bad for the batt. That's why even if you're using the fastest charge option on your phone, by the time you hit around 50% it starts slowing the charge rate down. The phone is programmed to do that to save the battery from degrading quicker. A custom kernel and OS could change that.

I'm sure, but how are they actually supposed to know that? You unlocked your bootloader, installed something like twrp, and obtained root access to jiggle with anything you want at that point. I used to have a lot of fun doing all that type of stuff, but I knew I voided out my warranty doing it unless I could still roll it back to factory and remove root, first. Not to mention dealing with knox.