Hi everyone,
Sorry for the recent radio silence.
Yes I have updated the TouchKeys software for a more recent JUCE, and it ought to be easily possible to make an updated build for Linux. Time being scarce right now, I'm not sure I'll get to that soon, but I will post a link to the code here soon once I sort it out (can share it privately with anyone who wants it in the meantime).
Regarding filing down the edges, yes you can absolutely do that. Even if the copper is exposed, it should still work fine.
I made a prototype keyboard a few years back where I got a professional model shop to take each key, sand it down and spray it with several layers of hard-shell automotive paint. The result looks and feels exactly like an original keyboard, and the sensitivity is still good. It was a laborious process though and very expensive even for 25 keys, so it's not something I'd recommend for the faint of heart.
BTW because I have received a few queries about extra TouchKeys kits: I'm completely out (I have spare parts, but not enough to make a full kit) and it's also really challenging in the current semiconductor market to make any more, because basically all the microcontrollers I would need are perpetually out of stock with long lead times. So I'm sorry to say that I don't expect to restock anytime soon. If anyone gets in touch with me to sell one secondhand I'll direct them here.
Best wishes,
Andrew