I have a family member living on my property in a separate but adjacent living space, close enough together to share my router's wifi. She likes to let her youtube app endlessly autoplay talking head news videos at full volume due to her hearing loss, and this goes on for a few hours in the mornings. The sound through the walls is annoying but headphones block enough that it's a non-issue as long as I can load something to play through them. The real rub is that I also would like to do something on the laptop during breakfast and her neverending news autoplay eats up all the bandwidth I am paying for when I want to use it. I can't cut off her internet, but I could prioritize my traffic over hers in the morning so that I can load an episode of something and listen through headphones. Yes I know this would be a bit unscrupulous but I have already suggested she not doomscroll via youtube all morning, to no avail.

Setting up a separate ISP account for the adjacent space isnt an option for the time being. The router/modem combo is ISP-issued and locked down by default due to too many service calls from people breaking stuff in settings. As far as I know it is not able to be swapped out to an off-the-shelf due to this being fiber optic internet, plus I'm only so-so in tech knowledge.

Which leads me to the title, can I put the ISP-issued router in a faraday cage, connect my own router via ethernet and be able to control settings via that route? Any reason I shouldn't/couldn't?