Maybe you should save the Excel file as TXT (or possibly XML), and then script the GDL Object to update parameters in its instances based on values read from the file.
However, this may or may not work because you may have to used the PARAMETERS command in the Parameter Script in GDL, and what I don't know whether you need to open each instance so its Parameter Script is rerun and thus reads the values from the file. In that case this can be cumbersome if there are many instances.
Another option may be to use Grasshopper-ARCHICAD Connection to set those values. That may also be possible. I have not tried it but based on the capabilities of the Connection Add-On and Grasshopper, it may be possible to do.
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