From my experince the player might change but the role doesn't, what you want from the keeper stays the same?? Therefore you can still give specific instructions 

If you are rotating, you need to be giving simple rules they can all follow. Skill cards are one way to maintain common points (what's expected in each role), but then equally if you have multiple coaches in a drill can one of you support the goalkeepers, or is there a drill you can do to focus on a GK skill (coming off the line for example).