I am quite new to MK community, and I have seen the terms Leeku-tuned browns, leeku-tuned Vintage Blacks being used frequently. Can anybody specify what they mean? Also, assuming it is a type of tuning to an existing switch, what exactly is the procedure and how much difference does it make?
It just means that the switches were customized by Leeku. It's a typical job, when one is doing assembly services, to "tune" up the switches using aftermarket (lighter or heavier) springs, lubricating friction points and springs, and applying switch stickers and SIP sockets and so on.
Leeku is also a PCB designer from South Korea, so his name carries that weight. He's known for the PCBs found in various Korean customs, particularly the TX-series, TGR, Mira, some LZ boards I believe, the L3 Alphas PCB (Alps TKL PCB that's a.87 spec), and others.