yes, no balancing if the balancing voltage is 4.20V.
i got to thinking about how i have my lipo pack in parallel with the lifepo4 pack and i am thinking that if i drop the cell balancing voltage to 4.17V then i give up the top 2-3% of charge storage capacity, but i do not end up pushing the voltage of the lifepo4 pack up as high currently 88.2V/21S. so i can charge them both to about 87.5V/24S or 3.64V on the lifepo4.
maybe you can hack the charger voltage up. it should be possible, and maybe if we try to order something around the 4.17V level we can talk henry into including that in his production schedule.
imbalance doesn't really happen because of the use of the cell down to low voltage. that has not been demonstrated, just conjecture.
becoming unbalanced is a function of the self discharge rates imo. each cell accumulates a deficit of charge over time and the balancing current has to be sustained long enuff and often enuff to keep the cells with the highest self discharge rates close enuff in available capacity to allow the pack to store that amount of charge. so then the cell with the lowest voltage during balancing is the limit on how much the entire pack produces, or saves depending on how you look at it.
in effect the BMS 'pays for itself' by allowing you to store the maximum amount of charge possible in the battery by providing a balancing function.