How does the judge selection for GPs work? Can host federations invite whatever ISU-level judges they want? Or can they invite judges from any of the federations whose skaters will be competing at the event -- so there might be some strategy in deciding to invite, e.g., an Australian vs. a Swedish skater to compete?
The way the ISU rules are written it sounds as though the host country picks the judges using a process agreed with by the ISU.
7.3
Panel of JudgesThe panel of Judges in each individual event of the ISU Grand Prix of Figure Skating will consist of 9 Judgesof different ISU Members in each discipline if possible, but not less than 7 Judges. Only International or ISUJudges are eligible to serve in the ISU Grand Prix of Figure Skating events. Each Judge may participate inno more than two ISU Grand Prix of Figure Skating events plus the ISU Grand Prix of Skating Final.The Organizing ISU Members will invite the Judges based on a procedure agreed with the ISU.
http://static.isu.org/media/351567/gp-general-announcement-2016_17-final.pdf