Note 4 SM-N910C Trinidad and Tobago Kit Kat downgrade help.

I have a SM-N910C from Trinidad and Tobago. I am using in on At&t in the US and it works great with LTE and all. I would like to downgrade to Kit Kat 4.4.4 from Lolipop because of all the lag and bugs.

I would like to know if flashing the stock rom back to kit kat is going to mess up the basebands? I went to Sammobile and found the Trinidad and Tobago 4.4.4 rom in the link (it won't let me post the link but here are the numbers from the link (PDA and CSC) below is this the right rom?

PDA: N910CXXU1ANK5
CSC: N910CUUB1ANL1
Country Code TTT

Also I was wondering if I could possibly flash other countries roms to the SM-N910C or if it would mess up the modem? If it is possible which countries roms are the most US friendly?

(One thing I hate about the Trinidad and Tobago Rom is the date format is backwards compared to the US "dd/mm/yy VS. mm/dd/yy" and it confuses me all the time)

I just want to make sure I'm not going to mess up my new phone some how.

I'd appreciate and help!