How to safely swap dead cells in an 18650 pack?

Hey people, I recently damaged two cells in my 12S4P 30Q battery pack. Unfortunately they were the 0V and 50.4V ones so the explosion on those cells blew them open on each side.

Now my first pack from the negative end is dead (picture left side) and the whole pack only charges up to about 45V, 4,1V each of the functioning cells. I already received 4 30Q’s for my plan to repair, although I think I might have to swap the 1 cell on the pack on the positive side that also suffered damage (yet doesn’t seem to short that pack).

Unfortunately I don’t own a spot welder.

So can anybody give me any advice? Can I just remove the bad cells and swap them out even if the solder doesn’t stick too well? Will I need to also renew my BMS? Could somebody maybe even in central Europe do the spotwelding?