Yes, you just need to define the AGD56 datum, which is a set of constants. The rest is already implemented, and we ported all datum supported by PROJ.
Yes, and this is possible due to our design that attaches epochs to datum. We will add a new function soon that takes any datum and adjusts the epoch for dynamic updates. There is an issue already for this: Add epoch shift to datum · Issue #41 · JuliaEarth/CoordRefSystems.jl · GitHub