Odd battery wiring? Shunt? change wiring on old AGM's?

[intervivos]

The battery bank on my Beneteau is wired a bit funky, see pic. Anybody have insight? At first I thought it was wired this way for balanced charging, but I don't think it accomplishes that goal. Should I rewire this now (I am installing a battery monitor shunt) or should I wait? If I rewire the order of the old AGM batteries could it cause issues?

My gut is telling me to let this live as-is for now, just take the negative to the battery off the negative switch and connecting that to the shunt, then getting a cable to run from the shunt back to the switch and be done. When this bank bites the dust move to lithium and install bus bars to clean this up.

Thoughts?