Unlocked 900A from At&t to metro pcs / T-mobile successful But can I root/rom it?

Hello if anyone could point me in the right direction, it would be appreciated.
Basically I unlocked an At&t s5 900a to Metro pcs yesterday, everything seems like it's working but the phone is still on the 4.4.4 stock At&t rom, can I root / put a different rom on it being that it's originally from the At&t network / phone? If so, would I need to put a metro pcs rom on it or at&t rom? I really just want to de-bloat the at&t apps and have it rooted so i can tether it. Anyone have any insight on this?

Flash Tmobile H631 Rom into Metro PCS LG G stylo MS631 device

I have a Metro PCS LG G stylo that's rooted and unlocked, running on the T-mobile 30 dollar plan. I want to be able to use WiFi calling among other apps from Tmobile. Can I use TWRP to flash the Tmobile rom into the phone?

Flash Tmobile H631 Rom into Metro PCS LG G stylo MS631 device

I have a Metro PCS LG G stylo that's rooted and unlocked, running on the T-mobile 30 dollar plan. I want to be able to use WiFi calling among other apps from Tmobile. Can I use TWRP to flash the Tmobile rom into the phone?