Today was a little breakthrough for me because I finally tried a Dimarzio Air mod on a Duncan pickup. I also used a UOA5 in place of the stock magnet. I got some interesting but predictable results and I think some of you will be very interested in this.
First of all, the 59/Custom with UOA5... What does it do? Well basically it takes some of the modern edge off. I don't think the top end is reduced at all. The highs do seem "softened," but the same amount of top end is still there. As usual, some of the low end and output is reduced with UOA5. As far as I can tell, it becomes what I would consider a "hot vintage pickup." What I mean by that is the "classic" qualities are a bit more emphasized and the modern edge is softened. The output is reduced a bit but still hotter than your typical vintage pickup.
I think it does sound pretty cool, but I still find the pickup to have a very loose feel and bright top end quality. UOA5 isn't going to make a drastic difference. Is it a better pickup after the magnet swap? Well if you want a modern twist on a classic pickup then no. If you want a classic twist to a modernized pickup then yes.
Now the Air mod. I had a left over set of plastic rings and smaller A5 magnet which seemed to have no problem installing in the pickup. It pretty much went back to the way it sounds stock except that some interesting qualities came out. I think the result is similar in a way to the UOA5 mod, but better. The smaller magnet didn't seem to reduce the output any, and it's basically the exact same sound as the stock pickup except that everything is softened a little, it feels a bit more natural and not so slippery-slidy loose as much as before, and it a bit cleaner in the way that an Air Norton is.
The bottom line: The UOA5 mod didn't impress me, but was nice; and the Air mod is almost a must-have.
I don't know if there is a way to substitute the plastic rings with electrical tape or some other kind of plastic or rubber material. I hope someone with that kind of knowledge could chime in and offer some explanations about the materials and how they will affect the magnetic field.