1. Add kws in new adgroups, but leave old kws "as is". Remove old kws when new group starts to move well.
2. Add kws in new adgroups, raise the price in the new adgroup and remove old kws.
3. Keep related kws in their adgroups and remove the unrelated kws to new adgroups.
Anyone have any other ideas that may work better?
I'd certainly suggest protecting yourself by leaving your existing groups as is until you're comfortable with the switch...
But, restructure away... adjust the bids slightly lower in the old group... and monitor from there. My guess is - you'll be fine. I've restructured groups within accounts with significant history countless times without any negative impact.
Good luck.