Hi,
I am also interested in this question, i.e. how to transform (in realtime playing) the recived midi velocity to a different value.
A very basic example in pseudo code: transform the Midi input velocity to maximum(Midi_input_velocity, 50).
More general transformations of this type are availabe in Ableton and FL Studio, see e.g.:
https://musicianshq.com/how-to-fix-a-qu ... -keyboard/
I guess what was stated in the initial post as "custom base velocity" describes is in fact the fixed velocity which one can set by double clicking on the velocity value (--) in the input section of the midi tab of an instrument.
Maybe there are other ways currently available in LMMS to achive a non-fixed velocity changes as in the above maximum example? I haven't found these yet - but I am an LMMS newbie. Hints are welcome.