Do cables need to be re-broken in?

Electrons become slow and lazy after just sitting around for a while.

Of course. Only its minutes not months, and movement matters more so than time. In other words your system warms up every night, and all the wire not having signal running through it is a part of that warm up. That's with nothing being moved around. Moving a cable around, all the bending and flexing, it will be a few to several minutes settling in after that. Try it and see.

When the music sounds like it’s slowing down I just rub some Geritol into the cables nice and gentle like. Makes an electron feel like gettin up and going.