Question

Which would be larger: an atomic mass unit based on current standard or one based on mass of a Be-9 atom set at exactly 9 amu?

Answer 1

$Be$ would be lighter on this scale than it is on the $C-12$ scale

However

Nature would not be changed by this new definition " the ratio of masses between any two given atoms of elements would be the same".

So,

The measured masses of all atoms would be slightly less by this new definition

an atom twice as heavy as $Be$ would now weights 18 as opposed to 18.02 by $C-12$ standard.

Of course, the mass of the atoms have not changed in an absolute sense.