Probably you want:
transform(groupby(data, :uniqueID), AsTable(All()) => complex_calc => "newname")
if you want to work with all the columns.
However, note that in this case you can also just do:
[complex_calc(x) fo x in groupby(data, :uniqueID)]
(in which case the result will be a vector not a data frame, but sometimes you might prefer that.