Turning a monophonic instrument into a polyphonic instrument in X steps

Ansgar has  been a hurdy gurdy player for 13 years now, he always wondered if one can build a polyphonic hurdy, that can play multiple different pitches at the same time. Instead of building an instrument from scratch, he decided to modify his own instrument by exchanging easily replacable parts:

He  build a second row of keys into a new lid that I could easily attach to the instrument, that operates the 2nd of the two melody strings that were there in the first place.

Additionally there is a spring-loaded mechanism that will activate the 2nd string only in case someone presses one of those additional keys.

While he is far from done, his current instrument greatly enhances what he can play on the instrument, and Ansgar would  like to share his  passion for little mechanical soundproducing boxes, the initial idea and how it evolved over time, some good Ideas (and some Ideas that turned out bad), and the message that EVERYONE should consider modifying their music instruments in the way that suits them best.