I fitted a pair of front panel toggle switches to our SCA N72's and J99's so I can easily change both the mic input transformer impedance and the output transformer loading without having to remove the modules to change the jumpers on the PCB's. (Haven't labelled them yet)
I'm finding I often prefer the 300 ohm setting on the mic input transformer even with our LDC's as it warms and fattens up the lows and is usually a little less sibilant than the 1200 ohm setting and can provide more of a vintage vibe if that's what you're looking for.
It also allows the singer to back off the mic without the low end getting too thin.
For those who haven't tried the 300 ohm setting I can recommend it especially if you need to take the edge off a bright condenser and thicken it up a little.
Don't worry too much about the 1 to 10 mic input impedance 'rule' just follow what sounds best.