question re adding a domain during trial

Hi,

Probably a simple question but I am trialling plan P1. I have uploaded some local folders but want to add a domain I own during the trial.

Question is; if I add my domain, will I still have access to the folders and content stored under the me@domain.onmicrosoft.com email?

There is also the question of whether it is wise to add a domain during the 90 day trial but I will only do that if I am almot certain I will go ahead with purchasing the plan.

Thanks!!