Please allow me a dumb question. There are so many printable add-ons to the extruder (AMS Hub fixers, cable fixers, Y-splitters, etc.) and to the Z-axis bar (lights, Panda breeze, holders, etc). What do you think… do these added weight might affect the precisity and function of the printer? I mean we are speaking of sub-millimeter precision… wont any added weight will be a plus strain and decrease function?
Welcome to the Forum. 
That’s what the various calibration routines are for. My printer even tells me when the belts need to be adjusted. The “shake test” is particularly annoying. 
Ehm. No.
Calibration tries to compensate for weight and resonances, but will never be as good as just reducing weight in the toolhead. For minimal ringing, VFAs etc. the weight of the toolhead should be as small as possible.
That said, it’s still possible that modifications actually improve prints: For example, if a bigger fan duct leads to much better cooling, it might offset the negative effects of the added weight. But you have to try and see if it does what you think it does…
Myself, I’m pretty happy with what Bambu provides and haven’t added anything to the toolhead.
What do you think of the new Biqu Panda Breeze? Custom laminal flow ventillator attached to the Z-axis bar? What filaments or scenarios might benefit from extra airflow?