Replace with "calculated" Piece?

I am creating an extension to VASL - and want to replace a piece with another. However the piece that should be put in place needs to be dynamic - specifically in this case the concealment counter for a previously chosen nationality.
I see that I can select a specific piece (or define one) - but can’t figure out how to make it “calculated”. I can’t just define a dynamic piece (that would be used instead of the standard VASL concealment) because VASL treats concealment counters specially in java code.

The painful brute force solution:

Create a Replace with Other trait for each nationality using the appropriate concealment counter

Create a Trigger for each nationality that executes the correct Replace with Other key command if the “previously chosen nationality” matches

Ouch. I was afraid of that…17 different “nationalities”, so that would end up being 34 new properties on this one counter. What would it take to allow a variable in the concealment counter’s “type” property? Like this: