You can only be a member of one Primary box in SugarWOD a time. If you belong to a few boxes and drop in to different ones during the week, you can switch your gym each time you visit to log workouts and participate socially in each community.
If you have coach permissions in one gym with your account, and athlete access in another, you can also change your Primary gym each time you visit. You will not lose your coaches access when you switch gyms.
You can find instructions on how to switch your gym in SugarWOD here.
Your workouts, PRs, etc come with you when you change gyms. You will not lose any data.