Lamy nibs can be changed, but the feed was not designed for that. A few times during a lifetime but not every five minutes. It needs some skill to do this job.
1) the nib is metal, the feed is plastic. They are held together by friction. Something is going to wear.
2) the nip end of the feed is designed that it pushes slightly against the nib. Plastic flows over time. The pressure reduces and you end up with a snug fit between feed and nib. No gap, no drying out of ink.
3) components come with tolerances. A slightly different nib may push the feed (elastically) more and when you replace the nib with another one, you may end up with a gap. Depending how big (up to 0.3) the feed will relax and close the gap, again. May take a few days or week.
I would recommend if you need different width and you doing it professionally, why not get several pens...
Feeds and sections come with tolerances. At the top and bottom of the feed and at the circumference of the feed where it meets the open end of the sections are tiny ridged, which are meant to deform, get squashed to compensate for the tolerances and guarantee a firm fit. This will vary. Feed and section are made from similar material and under pressure they fuse. How much depends on the pressure and the time period. Pulling the feed out rips or rubs off those tiny ridges and the fit will become looser. They are not meant to be taken out.
Hope that was not too much.