Start w/ new number then port later?

I currently have AT&T, but used Visible in the past and thinking of switching back because I recently moved and coverage is different. My question is, if I start with a NEW phone number so I can run dual-SIM with my main # on AT&T and the new number on Visible, can I port my number in place of that temporary/new number later and keep the Switch26 promotion and referral credit? I'd like to run both numbers for maybe a month or two before completing the port, just to make sure it works well everywhere I go.