The number 4810 is neither a size nor a type designation; it refers to the height of Mont Blanc measured in metres. It appears on virtually every Montblanc gold nib, from the small nib of a Mozart to the large nib of the Meisterstück 149. The 4810 imprint therefore tells you nothing about whether a nib will fit a particular model. What counts is nib size and the design of the section alone: the big 149 nib fits only a 149 section, and the nibs of the smaller Meisterstück models differ in size and seating.
Changing the nib yourself is not to be recommended without relevant practice. Nib and feed are a press fit in the section; pulling them out easily snaps off the fine fins of the feed, and a nib that is not seated exactly will scratch, go out of true or flood. If you want to change the nib width, it is better to have the job done by a workshop that specialises in pens. A nib exchange at the manufacturer costs so much that it comes close to the price of a second-hand Meisterstück — which is why some collectors instead buy a used pen in the width they want and pass their own one on.