[Q] Installing CM12 ON MY VERIZON SGS3 topic

Okay so I've been having an SGS3 with me lying around, but always love using it. It has TWRP on it and uses the app HIapn global so I could use T-Mobile on it. But I've been wondering, if I Install CM 12 on it will it erase the apns and not be unlocked? Because I can't stand touchwiz in anyway. Its on 4.1.2 with TWRP on it, Sch- I535. Will the phone also be bricked in any sort of way, because I've heard the new boot loader on the s3 makes it impossible to install a custom ROM. If anyone could help asap, it will be appreciated . :good::) I just don't want my T-Mobile service gone :)