You could in theory do that, but be mindful of the impedance transformation. If you used a 1:10 SUT, then you want your MC inputs to have ideally 470 ohms impedance, so that with the SUT hooked up backwards, the MM cartridge sees 47K ohms. I don't know anyone who ever tried it.
step-down transformer
Is there such a thing as a step-down transformer for phono cartridges? I have two MM cartridges, but my preamp has only one MM input and one MC input.
Can I simply connect to a step-up transformer backwards, ie, cartridge output to the normal transformer output and feed the normal transformer input to the preamp?