It sounds like you have designed the importer to generate a module that will act pretty much as the ordiginal ADC2 module did.
But now, someone has decided that they would now like to modify the generated module to make it ‘better’, but the generated module is not easy to change.
Just an idea, but I would have handled this by building the ‘flip unit’ in a prototype and then reference the protoype directly in the ‘Replace with Other’ definition (ie, Just a BasicPiece with no image and a prototype definition). You will then not have a reference to any units in the palette and the designer could move units at will. You could also add a standard unit to the palette using the same prototype, but it would be independent of the ‘Replace’ definition.