You can have two watches and keep all your customizations, but from my findings it does take time to switch back and forth.
You just need to unpair the current watch, then pair the second watch it will ask you if you would like to restore from backup of the first watch, you can keep doing this back and forth.
The only thing I have noticed in doing this myself besides the time it takes to restore whichever watch you are going to use is that you lose that days "activity" data. Maybe i am doing something wrong. Just reporting my experience.
Cheers