According to several sources, it is not possible to turn it off without mods or console. So I'll describe those two.
The two methods mentionned here are two among many. You may find other sources doing the same job.
All commands are to be typed in without first and last quotation marks only.
- Open the console with grave/tilde (left of your keyboard).
- If you want to remove/add a perk type "player.removeperk code" or "player.addperk code". If you want to remove night person rank 2 specifically, type: "player.removeperk 001d2495".
- If you want to remove other perks, or if you want more info on other codes, you can type in "help "name of perk" 4". It will give you all the console codes for the night person perks.
Concerning achievements, a Steam user says you can use the console as much as you want, nothing is blocked when using it.
Simply follow the instructions given on source page (link above) to load the mod into your game. This mod removes only the Night Vision effect, and keeps all other bonuses this perk may give you. There is no info whether this mod blocks achievements or not.