I also thought about replacing cells in some old packs, no OEM batteries available.
For nickel strips nkon proposes a service for spotwelding them at 0.5€ per cell, very good price IMO, with some cells at 3€ the whole thing wont be very costly.
But If you’re not in Europe that’s not helping.
About the potential bricking issue I thought about connecting another group of cell to the BMS during the whole replacement process, so that the BMS never see any cells going to 0V.