I've had good success with this snake plant that's 5 ft plus. But the soil is very old and is basically dust. It needs to be changed and I'm worried about damaging it. The planter will remain the same, but it's large and I'm not sure how to remove the plant without breaking up the root. Give how large the plant is, my guess is that it's actually multiple plants, though I'm by no means an expert on plants including snake plants.

I'd really appreciate help with how to dump the soil in there and replace it without damage to the plant.

As an aside, I'm curious why at least one of the healthiest leaves has curved like that. You can clearly see it on the right end of the plant. I have another, smaller snake plant where there is floppy leaf like that to the side but that seems floppy and unhealthy, whereas this leaf is very robust and seems healthy but it curved to the side (rather than, say, floppy like the other one).