If tier one is activated can it be deactivated?
Once active does it make everything in game harder?
If it can be deactivated do you keep any rewards you have unlocked and does the game difficulty go back to normal?
You can activate it anytime and you'll keep the Rewards earned if you deactivate it.
If you play in Tier Mode everything gets "harder" the more you progress through the Tier Ranks. Enemies will spot you faster, do more Damage and take more Damage, so you'll be forced to play more carefully.
Some weapons even become noticeably weaker if you deactivate Tier 1 mode. I unlocked the Sniper rifle in Tier mode and it one shots all helicopters and vehicles. but if you turn off tier mode it no longer does that.
Probably not. On the German forum, one user mentioned he reached Tier 1 one week ago, and I sincerely doubt he was the only one. I have no idea how to find out for sure, though.
First person in the world to get Tier 1? Is it possible to find out?
There's plenty of people who have already hit Tier 1 within the first few days of release. There's not way of finding out who hit tier 1 first however.