I haven’t seen an adjustable cutter; and I’m wondering how many gold bars would need to be cashed in to be able to purchase one. The single size units are pretty expensive as it is. I made my own, and with a little help from a welder you could do the same, albeit not one that is adjustable.
Measure the inside diameter (ID) of your pot horizontally and vertically. Acquire some small diameter stainless steel rod, and have it welded into a rectangle that is a couple mm’s short of your width and a few cm’s greater than your height requirement. Then tie monofilament fishing line onto it to the dimensions you want to cut. I filed notches in the sides of mine so that the fishing line would not slip out of position. And, presto, you have a terrific cheese harp. After making your vertical cuts you simply slide the harp into the central cut and rotate it at least 180 degrees to make your horizontal cuts.
I suppose you could restring it for different sizes, or you could make several of them.