My definition references blocks and figures out some geometric properties of the geometry they contain (namely beam sections and lengths).

This is all figured out and works well. But now, I want to assign Keys/Value pairs to the geometry in the blocks, based on what the definition has figured out.

…is that at all possible ?

What seems even more challenging is that the geometry is inside a nested block ; therefor, there are no actual instances of the block containing that geometry in my model.

There are just blocks containing blocks containing the said geometry.