The Custom line of pickups are available stock as the Custom (ceramic magnet), the Custom Custom (A2 magnet), and the Custom 5 (A5 magnet). One of my favorites is the C8 (a Custom with an A8 magnet). It's a great pup no matter what magnet is in it.
It has a bold tight thumping bass, present but not overwhelming mids, and screaming highs. Output is hot.
I personally like it. Often described as a PAF on Steroids. I think it is more than just steroids. Great Rock/Hard Rock/Metal pickup, but Flexible with volume control.
Only if you're changing out the ceramic in a Custom (with a regular ceramic). If you're changing any other (alnico) magnet to the dble ceramic you will get brighter, thinner, scratchier, brittle highs