Hello Geoffroy,
I find this in the documentation:
.permanent = bool
Get or set whether this responder func is persists when the user executes Cmd-. If false this will be disabled and removed from the global lists. The default is false.
Arguments:
bool
A Boolean indicating if this object is permanent.
Returns:
The getter returns a Boolean.
I think you could try:
~test = MIDIFunc( /* bla bla */);
~test.permanent(true);