Pol,
this is similar to an ESERO activity called “The Ice is Melting” that looks at the difference between melting sea ice and land ice.
Sea ice floats in water, so when the iceberg melts, it fills in the space that it was already occupying.
Water in a glass will increase in volume when it freezes, but there shouldn’t be an increase in volume when ice in water melts.
You could modify this plan to mark the water level before you add the ice – and then you are showing displacement in action. However, when that ice melts, it will not increase the volume any more.