This is more of a thought experiment, as I don't know if I'll have the time to work on it.
Looking at the Instructable, that seems like a fairly interesting and robust circuit, originally developed by one Tim Nolan whose website no longer seems to exist.
I'm somewhat lazy/fearful of messing things up when building from scratch, so I like to get preassembled modules and tinker instead. So, my thought is simple (ish). Looking at the LM2596 module, the output voltage is determined by the setting of the multiturn pot. I'd like to replace that pot with, say, a PWM controlled voltage from an Arduino, which I can then adjust using Tim Nolan's code to achieve MPPT.
So to be very specific, the question is: can I safely remove that pot and use a PWM'd voltage in its place, in order to control the output for MPPT?