The Grasshopper connection is currently limiting in the sense that information can be read from Archicad, but only Geometry sent/created through the link can be adjusted.
It would be amazing if such a basic thing as having full parametric control over a model or parts of it would be possible. Sometimes it's really just about updating some parameters or properties in Archicad, not necessarily about the geometry.
One example here:
Re: Use Object from library returns Null - Graphisoft Community
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