It should be as simple as going to Admin->Games->Games Played and changing your server there. As for raid tracking, that might be a bit awkward during the transfer. Tracking in game should be no problem, but when importing that raid you may have to do some manual work to get it all lined up right. I believe the system will see them all as new characters? I haven't tested that myself to see what all happens. It should be pretty straight forward and hopefully not too time consuming. Let me know if it gives you issues when you get there!
Ooooh good point. I think I might just have to stop actually doing the raid progress uploads until everything is sorted, then go from there.
Everything is a bit up in the air at the moment, as Guild Transfer has been withdrawn from the shop temporarily while they fix some bugs. But we're planning on starting the move this weekend anyway so .. if the guild transfer goes ahead, then hopefully the majority of people will simply move from one realm to the other. If the guild transfer isn't available this weekend, then a lot of people will move over anyway, to a temporary guild, until we can get the new guild transferred.
So once the guild has actually been shifted, I'll do a roster update, which no doubt will tell me everyone has left the guild .. but also joined the guild with a different character name? Once I've sorted all that, then I guess the uploads from the addon should work again.
You shouldn't have to stop uploading raid tracking logs before/during/after the transfer. It may take a little bit more manual work if some characters haven't transferred yet while others have and you still do a raid. It would recognize the characters still on the original server, but recognize the characters on the new server as new characters. You would just need to deal with that as they happen on each raid upload.