The Grasshopper-ARCHICAD Connection never modifies already created elements the way ARCHICAD does. If an ARCHICAD element was created by Grasshopper, and the Grasshopper source changes, then the previously created instance is deleted and a new instance is created.
You can see this by creating a Wall with Grasshopper, and dimensioning it. The dimension will be associated to that Wall instance.
If you modify some parameters in Grasshopper, the Wall is removed, along with its associated dimension, and a new Wall instance created.
I think most (probably not everything) of what you want to do could be done using the Find & Select Palette and/or with Graphic Overrides.
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