The Sachs/Sram IGHs use a clickbox containing all the indexing gubbins that slides inside the hub. To remove it you pull it out and to reattach the cable you push it in, thats all.
My Shimano Alfine seemed OK to remove in a practice run on a summers day. No cables to unbolt, just unhook the cable from the gear changy thing (cassette joint) as
illustrated. I can see it being more difficult with frozen fingers. Shimano recomend you keep a small allen key to engage a specially placed hole to rotate the cassette joint