Theorically it doesnt vote any warranty, but to play it safe Honda SC might void your electrical wirings if they are finding something to blame for. I think better wait for after warranty only install the foglights to avoid any hassle.

You can, but I wouldn't advise you to.
#1, you'll need the fog lights to begin with. Original honda part for that not cheap. Last i remember, almost 1k
#2, you need the bumper with the cut out.
#3, wiring harness
#4, you'll need the switch. For old City and Jazz no problem cause fog light switch used to be on the dashboard panel the 3 empty switch holes there. for new city/jazz, it's on the lights/indicator stalk.

So unless you are willing to spend this much on getting foglights and with proper installation, it's just not worth it. Personally, i wouldn't waste my time and money with those shops that just cut out a space and put on any button at the dashboard switch board.

And also, original foglight shines to the corners. it doesn't shine straight. you wouldn't miss it. better u invest in DRL than to retrofit fog lamps.
Btw, I think i owe someone some pictures of my NHC with crystalvision on both lowbeam and fogs right? hHAHA
post later tonight. tomorrow labour day. got more time on my hands tonight.