Help regarding Un-Rooting my android device

Hey Guys!

Initially I used to have a HTC one, but due to an issue with the camera, I had sent it to HTC. And my dad was thinking of getting a new, relatively cheap phone. So i got the micromax canvas 4 (India) [ Just in case anyone is interested, I have the white one: http://www.smartprix.com/mobiles/micromax_canvas_4_a210_-m3334.php?tab=specifications ] and the phone has been pretty solid for it's price, all but the camera. And just having fun, I rooted the device and tweaked everything (but didn't flash a custom rom though). I also have my Google account associated with it. But now that my HTC one is back, I've got to give back this phone to dad. And since I knew this day was coming, the past few days I removed the apps which only I use, and installed a lot of apps that my dad would be needing. But I'm now facing 2 problems. First, I'm unable to link the device to his account and remove mine. So my first question is, how do I do that without performing a factory reset??

And another problem is that, when I told my dad that warranty is lost, he gave me a stern look, and asked me remove root. So again, it looks like I've to do a factory reset. But I'm too lazy to the complete procedure of customization I did for my dad. So is there an option to get back to stock by backing up everything and un-rooting the device??

TLDR:

1. How to change the default Google account associated to an android device??

2. How to un-root an android without losing all the apps and non-rooting related changes I've made to the device??