THIRD STEP
Calibrate the core using NFE Core 2 (Many many thanks to nicesoni_ash, without him i would've been stuck with a dead phone after flash with modded rofs files)
Open NFE Core 2
#1 Click on the "Open" button and select the core file to be calibrated
#2 After the file is initialized click on the "ROFS calibration" button
#3 A popup window appears, change all values to "2C"
#4 Click on "Apply"
#5 Click on "Exit"
Nothing else needs to be done in the core file
FOURTH STEP
Flashing the phone with the modded files using Phoenix (Thanks to nicesoni_ash again, this procedure is entirely based on his method as he posted as a document)
IMPORTANT
#1 BEFORE FLASHING, EVERY IMPORTANT DATA FROM THE PHONE SHOULD BE BACKED UP
#2 THE MASS STORAGE CONTENT SHOULD BE BACKED UP TOO, AND IT SHOULD BE FORMATTED
#3 IF NOT FORMATTED DELETE THE SYSTEM FOLDERS FROM MASS STORAGE
#4 THE PHONE SHOULD BE SWITCHED OFF BEFORE STARTING FLASH
#5 PHONE SHOULD NOT BE CONNECTED TO COMPUTER UNLESS INSTRUCTED BY THE FLASHING SOFTWARE
Open Phoenix
Now follow the pictorial instructions
Now bring all the original downloaded firmware files into the above mentioned folder
To do this, create a folder named "RM-xxx" inside the above mentioned folder, where xxx is the device's number, and paste the files inside this folder
According to the example the files should be in this folder now - "C:\Program Files\Nokia\Phoenix\RM-xxx\"
Now follow the rest of the guide...