K8028 / K2657 Preset Level

I note from your website that Project K8028 is a replacement to previous
K2657.

There is, however, one feature that is missing from the K8020 design.

The K2657 allowed for a preset minimum level via RV1, the K8028 appears
to not have this function, is it possible to reprogramme the PIC controler
to facilitate this, or to place a modification direct to the design?

No, this is not possible.
This was not a feature on the old K2657 but a calibration.