Yes, in the ednd my goal is to increase my battery life. I pretty much only watch youtube videos anyway. The only thing I could do is activate "Stanby intelligent power saving" wich I don't really know what it does excepted that it does something in standby, haha. I also activated/unhidden the developper options by pressing a few times the build number. I din't modify anything because there wasn't what I'm looking for. I only checked a bit on google on how to root, but I rapidly stopped as websites looked a bit suspicious to me. My phone isn't rooted as far as I'm concerned.
Also, when I say underclocking, I mean going down from 1300Mhz cpu clock to, let's say, 500MHz, not some little underclock that does not really make any difference. Also, I'd maybe even like to limit my phone's refresh rate as well as reducing the screen's resolution.