My Rooted Note 4 needs a new carrier I have a galaxy note 4 from T-Mobile the phone is rooted. Now I need to switch carriers to At&amp;t. I have the code to unlock the phone but I need to know (if I put the new at&amp;t Sim-card in my phone will I brick my phone? Do I need to unroot phone?) The phone is running stock rom t-mobile right now.
Putting in the SIM will not hurt your phone at all. Even if you don't have the unlock code, your phone will be fine. The unlock code just allows the phone to be able to read the SIM of the other carrier. 

You do not need to unroot, nor do you need to do anything beyond entering the unlock code.

T-Mobile is a great carrier when it comes to giving customers the unlock code for their devices. Usually as long as you are in good standings with T-Mobile, and have been a customer (I think for at least 90 days) they will give you the code.