Hello and welcome to the forum:
Easiest way to ‘bench balancing’ cells is to connect them in parallel and let them equalise over a few days before putting them in the car. Charging will end once a cell reaches 4.1V, therefore balancing beforehand is essential.
Due to different cell chemistry the BMU will have great difficulty adjusting the capacity (if at all) easier and quicker to tell the car that a new battery has been installed. Instead of a MUT3 you can use a Lexia/Diagbox clone to perform this task, see discussion below.
https://myimiev.com/threads/i-miev-and-lexia-3-and-diagbox.4042/
Nice car btw..
Mickey