I got a new (second-hand) bike this week. It’s got swept back handlebars and I just don’t like them after riding with them for a few days. It feels like I’m holding onto a zimmer frame and I hate how I have to hold my arms to the sides 
I wanna replace em with cool, non-lame handlebars like these 
l will almost certainly need longer cables for my brakes and shifters though. How much of a pain in the ass would swapping out the cables be?
Not hard at all. You just replace break and shift cable with a longer one and then you have to tension it right. Check out cjhoyle on YouTube. His maintenance playlist have almost everything you need.
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy: