Changed head and now printed parts don't fit

I have a P1S.
A few months ago, I had a meltdown of my print head, not sure why. But BL promptly sent me a new nozzle. They didn’t need to though, as I had bought a hardened one for CF when I bought the printer, and so I put that one in, along with the hardened gears, etc.

The thing I loved most about the printer was that I didn’t have to leave clearances between pieces in my drawings. Everything fit with perfect tightness. PET parts complained a bit, but PETG were perfect. I printed a bunch of multi-piece objects, and they all tesselated perfectly.

However, after making the upgrades to CF-ready equivalents everything is a little too tight. PETG parts have to be filed down to fit, and sometimes still break, and PET is impossible.

I looked on the forums here and found lots of solutions, but nobody talked about an effect from changing the head, which I think would affect which solutions might be likely.

So if anybody can suggest some setting or alignment procedure to improve this situation, I would be extremely grateful. The printer is otherwise working just like before, which is to say flawlessly…

You changed the setting to an HS nozzle at the printer? Nozzle comes with Stainless .4mm nozzles and you need to toggle from stainless to HS at the printer. There was an issue a few months ago that prompted BL to change firmware because people were changing setting in BS only.
I do not mess with CF but have not seen much in the way of posts about fitment issues around fiber fiber filled material