Simple ? - Can I specify - somehow - an axis with a M220? I think that answer is no. It just seems I would prefer Z not to be super slowwww when I put it at 50% feedrate. Z is slow enough at 100%. My Z hops are slow up and down and they have default Accell and Jerks.
And for some reason OP says it can't read feed/flowrates. It isn't a firmware limitation.