Yeah, it’s gunna wreak havoc on everything! (Lol, well laughing, but not really but kinda). Only cause that’s why ya switched p/u’s in the first place, something different right? But there’s s lot at play here on how much changes, I don’t know what the specs are on those specific pickups but if your going from a ceramic 17k to a Alnico 2 9.5k it’s gunna be a pretty big change & could & should effect tone, feel & gain/output.
So yeah, how much it changes depends on a lot of different factors.
One thing is, don’t get discouraged if you’re not digging it right out of the gate.. give yourself the time to learn the new pickup. Sometimes just a little pickup height adjustment can make all the difference after you’ve re-dialed everything in & learned the pickup a bit. They all have a sweet spot. I’ve swapped pickups a ton of times, not cause I don’t like them, but cause I’m curious by nature & if it was an easier quicker undertaking to do I’d do it even more often for sure. It’s a fascinating fundamental part of the electric guitar, how magnets & wire work together. Cool stuff.