It depends on the bars. I did wild1s 578s on my 2011 Ultra. They are a 10.5" ape style bagger bar. I had to change the clutch cable. I BARELY was able to use the brake side cable. I may change it anyway one of these days.
I was able to re-route the wiring without extensions by cutting the looms loose and removing and re-taping part of the harness. It's tight but it works.
Anything 12" and up you'll be doing all the cables and extending the wiring. I don't see any way of getting around it.
You'll realize very soon that the stock cables and wiring have very little slack built into them so anything you get that's over 2" rise or pull back above stock will have to get extensions. I was able to get away with using the stock wiring on my '12 Ultra but had to get new brake and clutch cables.
Just installed 10" la chopper apes last night on my 14 SGS . These were not the twin peaks but did black bars and quality was very good, la said stock cables and wires and they did all work but it took some tweaking to make that happen. I would extend all if doing again for sure, I would much rather have extra than trying to figure out ways of re routing . Also factory fairing mirrors are 100% blocked, gotta do handlebar mirrors.
I re-used the existing wires on a set of fnb choppers 12" menacing apes and could have easily gone with 14" on my 16 RGU. There are some great video's on youtube that were very helpful. Also on the 16 you dont have to de-pin all the wires on the connectors.