I had to take the cables loose on my 89 to free up the movement. The nut was a simple plastic nut. I grabbed it with a pair of long nose pliers and sort of broke it loose, the rest I took off with my fingers. I had a little difficulty getting the needle out, but was able to grab it again with long nose pliers and it eventually came out. The other side was much easier. The cable had a junction where it splits from a single cable into two speparate cables going to each carb. I did not have to remove the assembly so cannot offer any advice as to how to do it. I will say that once I freed up the movement in the chokes, my bike will start in any kind of cold. Not so easy starting before the procedure.
Needle nose or if you can fit one of those crowfoot wrenches around stuff that's in the way ... it's 10mm I'd guess. I've done it both ways. The object is just to get the plastic nut loose so you can spin it with your fingers as Greg said. It you trash the nut it is very inexpensive to replace...so no worries.
Was just there for armour ss cable upgrade. Trick is to remove the rubber sleeve from the nut first. Then nut should come off easy after that. The choke pin is removed by retracting the spring and rotating off the cable end.