I would err on the side of caution and not extrapolate from Kevin Carter's practices with the Lundahl transformer to other transformers, which may have higher step-up ratios and be different designs. Putting a 1 volt signal into a 20 db step-up will result in 10 volts on an output that is intended to handle a few millivolts.
Good comments by JJ. Personally, though, I would not put a stepped up line-level signal into a phono stage whether it is turned on or not, especially if it is solid state. It's easy enough to get a resistor at Radio Shack or elsewhere and not take any chances.
Regards,
-- Al