Sometimes it's a matter of semantics, but many do speak of SUTs as if they have an impedance of their own. This is not the case, so I am sensitized to that implication. As I know you know, any transformer merely converts current to voltage (if you think primary to secondary), and the impedance seen by the cartridge is simply a function of the impedance present on the secondaries. The SUT adds no impedance. (This is in a perfect world; in reality there is a tiny effect that can be disregarded for loading a cartridge.) It's obvious that you have a handle on it, so I apologize for my pedantry in correcting your original statement. I just know some others might have been led astray and was trying to prevent that.
For one thing, if you have a cartridge with a high-ish internal resistance, like a Denon or some Benz cartridges, such that it is not an easy match for a SUT, there is no reason you can't replace the 47K resistor at the MM input with a 100K resistor or even higher, to make the cartridge happy with the final impedance it has to drive.