I have the GT bars on my R and i'm very happy with this setup.
I didn't do the swap over as I bought the bike with the GT bars already on.
I also have the original R bars complete with wiring loom, and looking at it, I would estimate that the areas that I might find challenging is:
If the wiring isn't already installed inside the bars, it's not going to be easy to fit the loom up through the bars.
Whilst swapping out the hydraulic hoses for longer ones isn't difficult, bleeding the brakes satisfactorily might be the challenge in that department.
Apart from that, I will be pretty straight forward......but don't rely 100% on my words.