Do M164 mixing ratios get stored to eeprom?
I change mixing ratios for T0 during print via postprocessing quite often.
Do I run into the risk of wearing out my eeprom?
Depends on syntax, see description
M164 S<virtNum> P<0 = dont store eeprom,1 = store to eeprom> - Store weights as virtual extruder S
So as long as you have no P or P0 it is only temporary. In that case changing a value in eeprom will override it as eeprom writes cause a reread from eeprom. Normally does not happen during prints so should be no problem.