My question is "Do these arms have detachable armleads?"
No. There is a plastic bung in the base of the arm, same one used on all current Rega arms. which is held in by a single grub screw. Remove the screw and the bung slides out revealing the solder joins on the back of it where the outer and inner cables are joined. It's easy to unsolder those and remove the outer cable. Audio Origami and others can fit new outer cables if you don't fancy doing it yourself.
It's worth noting that Rega, Linn, Audio Origami and pretty much every other tonearm manufacturer use different external and internal cables. I've spoken to Johnnie and about this and he explained that, in his opinion, single cable runs are stupid. There are several reasons.
The demands on each cable are sufficiently different that one cable is worse than two. One of the most important aspects of the inner cable is that is does not restrict the movement of the arm. On high-performance arms one of the main advances is the use of very carefully adjusted high quality bearings. The inner cable has to be very thin and flexible or it can impede that free movement. The outer cable wants to be more robust and a better, thicker conductor can be used as you're not constrained by the need to be super flexible.
If you look at the wire used in single-wire kits it's a compromise as there is no way you could use the internal wire in an RB2000/3000 all the way to the amp. It's far too thin, take a look in the gap between the arm and the bearing boss and you'll see it. So your super duper new cable is going to undo all the work Rega did getting the bearings as good as they can be. The arm will work, but not at the level it's designed to. Your internal cable is too thick.
Which leads onto the next point. If you fit the new cable yourself, the chances of you getting it dressed correctly so that it does not negatively effect the movement of the arm is close to zero. If you just pull the new cable through with the old one I'd say it is zero.
The internal cable has to be positioned very carefully so that the arm is totally free to move in all directions. It is not pulled tight inside the arm, there is a loop of cable just above the exit point on the arm tube. Also, there are rubber grommets in the arm pillar which hold the cable central and allow the top section of the cable to swing back and forwards. Pulling a cable through there is going to move those grommets, it might pull them out altogether. Without tools and taking the arm apart you're not getting them back in the right place, if you even know what that is?
And the whole point of this is what? To remove one or two solder joins from the signal chain? Your amplifier and digital kit probably have hundreds in them! If they were really such a disaster don't you think that all tonearm manufacturers would use single cable runs? They could, couldn't they? In fact many are complete idiots as they use plug connections at the base of the arms. The fools. Know they nothing?
I'm not saying that you cannot find a cable that is better than the one fitted out of the box, certainty on lower end arms. But the cable on an RB3000 is going to be pretty ok. I'd imagine any improvement you can find will be marginal if anything and you could make the arm worse.