In principle all diadems can be modified to fit the bearer best. The one diadem is ultra-flexible (Leuchtenberg!), the other maybe requires some more work because it has been fixed more permanently.
That is why I was a little bit disappointed with the way the diadem was worn by Princess Marie-Chantal. After thirty years one would think the whole jewel was controlled, cleaned and fixed to suit the Princess' head best. It looks like this has not been done. The picture by Maud shows that the diadem in any way is quite flexible.