Is this a scam?
Yes, it's a scam.
Is it possible for hackers to alter an old version of an official app to redirect users to malicious websites?
If so, how could they achieve this?
Most likely no. To do that, the hacker usually need to have access to your friend device. And if a hacker actually can do that, he would do soemthing else to steal your friend's coin, credential and other personal data. While i don't know how Jaxx Libetry works, i would speculate the hacker buy expired domain which used by Jaxx Liberty to obtain certain data from internet.