Upgrading pickups, replacing parts of the pickup? – Guitars Forum

I was thinking of trying to do some simple upgrades on leftover pickups from guitars where I have replaced them with higher end pickups, for example replacing ceramic magnets with AlNiCo magnets and replacing the mounting plates. I’ve watched some YT videos, I still have a few questions though

Where do I get these parts? So far the only sources I’ve found are chinese based companies with little information on size, postage and which seems a tad dodgy, and a couple of US based companies, postage from the US is so high that with added custom fees I might just pay for complete pickups though. I need a source based in the UK

Do I need to replace the poles when changing magnets? Can I replace the poles without rewinding the pickup?