Force mass value of an assembly

Hi all,

I have an assy of a electonic board, received from a supplier, with a lot of component that i know only the mass but not the other value like density.

If I try to change "define properties by" to fully assinged and write the value in the mass field and click OK, it will apear a message "Uncorrect Value".

The sistem wants all the parameter like density, area, inertia and COG.

There is a way to force only the mass value?

Thanks