The reprograming of the power module with the serial number and part number of the new battery is required because the part number tells the ecu the capacity in Ah, and the change of serial tells it to reset all parameters such as various counters, present charge state, ageing effect etc...
You may get away without doing these things, but it could result in an undercharged or overcharged battery and inaccurate battery meter reading, as well as premature or postmature entry into power saving stages and the new battery having a shortened life expectancy.
The coding instructions are on the Ross-Tech website, i also found this Spanish site useful, once it's been translated lol
https://www.audisport-iberica.com/fo...r%C3%ADas-vag/