Thank you all for the advice, I will carefully check the effective rim
diameter.

Now, since I am keeping the old hub, that contains a dynamo, and the
spokes, I will not exactly be building a wheel, just changing the rim.
To do this, a colleague of mine suggested a tip he used for doing the
same: attaching spokes together with some tape, everywhere they cross.
Then, after unscrewing the nipples, the rim can be removed while the
spokes stay in position. This way, the new rim can be positionned, and
nipples screwed back without having to position spokes one by one.

I will tell you how it turns out.

--
Tanguy