That is precisely what you can and should do. You have enough time to deplane; use the restroom; and then return to the same gate and participate in the mandatory security screening at the gate. Sometimes that secondary screening is limited. Sometimes it is VERY thorough.
Remember, the Public Address system in this airport is painful to the ear and incomprehensible. Moreover, I've seen them just start the boarding process without any announcement, and without any priority to first-class passengers. Truly.
I've experienced some great service on the E175 jet, both outbound and the return. If flight attendant Luis is working, you will be treated well. Just remember to bring your portable battery charger for your phone, and use Mobile Passport app for your smartphone for the return through customs in MIA.
Report back.