I had to install this software called AltServer to my PC and connect my phone via a cable every 7 days to keep the modified YouTube installed.

iTunes users can "refresh" apps installed through AltStore through WiFi but you still need to keep your computer on when doing it. I opted to use a cable because iTunes is annoying.

AltStore can install a maximum of 4 apps iirc but they expire if you don't refresh it. My friend paid for an apple developer account ($99 yearly) to keep AltStore on his iPhone so he doesn't need to refresh using a computer.