Question regarding Roms

I live in the UK and bought the SM-N920A UD which is the AT&T version
What I'd like to know is once Samsung release updated roms for the Note 5 could I flash a different rom onto the phone?
IE SM-920A, B, C etc Obviously a genuine Samung untouched rom - would this work? and would I then be able to root it?

Questions regarding Carrier Specific messaging services

So I use T-Mobile's new WiFi messaging service because I live in an are with no T-Mo coverage but the battery life is ATROCIOUS on stock T-Mo ROM's. Also the lack of Deodex means no Xposed (It bootloops after a couple of days). So my question here is, can I use a unified ROM like WETA or Xtrestolite while still using my T-Mo wifi messaging? Or is a T-Mo ROM needed? Thank You!

Questions regarding bootloader relock

So, I had my bootloader unlocked back when I was in kitkat (unsure whether I had version 4.4.2 or 4.4.4), but I had backed up my ta partition in case I wanted to relock the bootloader.

Fast forward to today, I am on lollipop (version 5.1.1) and I want to relock my bootloader. Note that I am on stock kernel.

Obviously enough, I have to restore my ta backup.

But I have some questions.

1)Do I have to downgrade to the android version the phone had when I took the ta backup, or I can simply flash the ta backup on my current android version?

2)During this procedure, does anything (such as data) get wiped?

3) Will I lose recovery during this procedure?

battery error regarding canvas 2 plus and its resolution

I have pure xperia rom on my canvas 2 plus.it's showing error continuously," your battery has too low temperature..please switch off the phone." Can anybody help me how to resolve this problem. Also battery is taking too much time in charging. And it goes up and down between 80%-100% very fast..please help me..