Iacopo,
Thank you very much. Yes I had been thinking about the modular spinning top idea, or at least being able to replace the brass flywheel as so much effort goes into making it! (as i'm sure you know) A 3 piece top: flywheel, tip and stem would be easy to make modular. The items can be press fitted. As you may know, with my early tops, the tips were held by bluetack! This may not seem great because there is a looseness to the top, however adjusting the tip is very easy. I used the paint technique to find the leaning side, and gently pushed the tip in that direction. After a few minutes, the balance would be decent. What i am trying to say is, I think maybe a modular top is a good idea as an experiment. Perhaps you might try making one some day. I'm sure you would do a good job.
-James