First of all … updating the firmware via VRM really is a breeze … it worked brilliantly with my 6 x US3000C.
A cell voltage difference of 30 mV is perfectly fine and would not be a reason to carry out an update. A few months ago, I would have advised you against it because of the possibility of the wrong firmware being used for an older or newer chip. But that has changed now.
The more important adjustment to reduce wear came through the GX firmware … and top balancing is still being adjusted … So far, this has usually been done via Node-RED … see Pylontech Ladekurve passt nicht