Does this mean simply enter the maximum value of MLHFM in MLMAX and the limitation is removed on software side?
No this is only the limit of pre-calculation for Display. You can change it, if you want to have for some after market Loggers more than the output of 189g/s.
On some ME7 you have MLDHFMKO which really limits your Airmass, if you cross that point Lambda is not calculated anymore.
They have "normal" factors, 16bit lohi, for kg/h use 0.1 or for g/s 0.027778.