Hello ahuber33,
Unfortunatly this does not solve the issue.
The command you wrote are used when you want to reinitialize the geometry but my problem was about the redefinition of the materials when the geometry is reinitialized.
Moreover, it is not necessary to include these commands in the detector construction because they are automatically called when the RunManager::ReinitializeGeometry() method or the equivalent ui command /run/reinitializeGeometry are called.
Andrea