Repeating what has been said here: you must replace the entire PrintTool rather than just changing the hotend
Also, @Josh-3D talks a little bit about ithere H3C First Impressions
and how he decided not to swap.
I originally was planning on doing a full 9 color print as part of my initial project. I test printed that 75a TPU first though before I started to swap that nozzle for a regular one. Oh, that TPU just blew my mind away though. As I got to the point of trying to swap the nozzle (You have to swap the nozzle+holder assembly when going from 2.85 to 1.75), I felt it a bit tedious of an operation. You have to partially remove the AMS top, which includes taking out some plastic screws (These should have been machine screws in my opinion), to get the data cable swapped. Basically, it’s not a quick easy swap. This is something I actually found frustrating, because as much thought went into the overall design, having that part be more tedious to swap. It missed the mark a little. Because of that, I decided to leave the 2.85 nozzle in there and adjust my design down to 8 colors. Or well, 7, as there was a PETG core to a PLA multi-color print, so my actual multi-color part only got 8 colors. TLD
Edit: Bambu really should have done a directed concise write up about this procedure in the wiki. Maybe they did and I missed it or maybe it is in the works. @SupportAssistant