I have an A5 Mule and I must say I'm really into it. Its been a few of my guitars now and its always sounded excellent, even in one particular Flying V where the Riff Raff was not quite working. Probably its my favourite single pickup.
I remember calling BKP and placing the order, it was a few years ago now, but I was ordering a bunch of pickups from BKP, all PAF styles ones. Anyway, we were chewing the fat on the phone (I assume it was with Tim at that time) about PAF tones and I was explaining what my ideal PAF would be, I said something along the lines of the Mule with that kind of warmth it has, but with the bite of an A5 magnet, and pokey in the mids. I remember Tim became a bit excited by this and it seemed like he knew exactly what to do to achieve this, we'll do you a Mule bridge, but with an A5 magnet, and close up the offsets to really bring out the mids for you. A stock A4 Mule neck was suggested to go with it. Anyway, the pickups arrived in the next few days and I couldn't have been more delighted with them! It does work really well with the stock A4 neck. As the cliche goes, it nailed the sound in my head.
Anyway, I also hear that this type of custom order is not really possible any longer. Some people on this very forum have suggested Cold Sweat or VH2 neck pickups in the bridge may or may not do something similar - I have no view on that, never having tried it.
Changing the magnet of an already wound pickup won't change the winds, and in my particular A5 Mule the wind certainly was changed.
There is a difference with the riff raff. The riff raff is a dry sounding pickup, thats one of the coolest things about it. I've had riff raffs in a couple of the same guitars as my a5 mule and somehow the a5 mule keeps alot of the warm mule sound - obviously not completely though, its all a trade off.
Its all kind of academic though if they won't be made anymore. I for one really like my a5 mule and would buy another if they were made available. I don't know if my particular pickup has something different done to it than other A5 mules, as they were all one-offs, so perhaps they were all a bit different.