Have I correctly identified the resistor that sets the phono input impedance?

I think R1 (left-hand side) sets the input impedance for the phono stage. It matches the manual's "50k Ohm" value. I presume I could change that if needed to match another cartridge?
 

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When you can listen to an MM cartridge with an amplifier where the phono load resistance is variable (e.g. from 10k to 100k) , you may come across some interesting audible findings
I have a mid-MC cartridge, specified for ">200 ohm" input impedance. I have a phono stage capable of loading at 47k, 1000, 500, 200, and 100 ohms. 1000, 500, and 200 all sound the same. 100 sounds a bit rolled off or "softer". 47k sounds a bit brighter, more "present"; might just be a bit louder?
 
MC is completely different kettle of fish - capacitance is irrelevant, loading should be significantly higher impedance than the cartridge, here 500 ohms is probably the one to go for.
A phono stage that tries to handle both MM and MC on the same input is rather a compromize, alas, since MM requires low capacitance, low current noise amp, MC requires ultra-low voltage noise amp. Something like a bootstrapped ultra low voltage-noise JFET can work for this, but its more common to see separate MC amp that can be switched in.