What I can't seem to find is an explanation of what the programmer is doing to the "blanks" to set them. Also curious if there's a way to program them without the manufacturer's device, or if that would be ridiculous?
MEMS oscillators (like the SiT8008B) include a special phase-locked loop (PLL), usually a fractional-N PLL, which generates a configurable and, within certain limits, arbitrarily adjustable output frequency from the resonator frequency invariably fixed by the mechanical variable. The necessary division ratios of the PLL are stored in MEMS oscillators together with the coefficients for the temperature compensation in a memory in the semiconductor chip. Programming this memory once sets the desired output frequency.
So the programmer is programming a portion of the memory of the blanks. I hope this (and Spehro Pefhany's excellent comment) answers your question.