Edit Sf2 features within Soundfontplayer via MMP file

Having trouble with LMMS? Ask about it here.
When saving a LMMS Track as uncompressed MMP (not MMPZ) File, it looks just like a XML File, which you can edit.
Typical lines for the Soundfontplayer look like this one:

<instrument name="sf2player">
<sf2player patch="0" chorusLevel="2" chorusDepth="8" reverbOn="0" reverbRoomSize="0.2" chorusOn="0" chorusSpeed="0.3" reverbDamping="0" chorusNum="3" reverbLevel="0.9" bank="0" reverbWidth="0.5" src="E:/SF2/Sonatina Orchestra/Strings - Basses Staccato.sf2" gain="1"/>
</instrument>


This is interesting, because it seems to give you the possibility to directly edit the parameters of a soundfont.
The soundfontplayer is based on Fuidsynth, which is known as a powerful soundfont synth, isn't it?
So, if one can change the parameters for reverb and chorus, shouldn't it be possible to also change the parameters for cutoff frequency and resonance (normal integrated soundfont features like reverb and chorus)?
This...

http://fluidsynth.sourcearchive.com/doc ... ource.html

...looks like as if this is possible.
Cutoff frequency and resonance are not implemented in the LMMS Soundfontplayer GUI.
Nevertheless I would like to edit them. Would be good if this works and brings back the brilliance that is lost otherwise.

But how is the syntax in the XML-File of LMMS? I tried cutoffFrequency="2" resonance="4.5" without success.

This could be useful also for Linux' Qsynth, which also just have knobs for reverb and chorus, but not for cutoff frequency and resonance (can someone tell me why?).

PS: I don't want to use Plugins for editing cutoff frequency and resonance. I want to change these features direct within the soundfont and not on a second level. This would be like turning the sound knob of a guitar down and trying to get the treble back with the equalization of the amplifier.
IIRC, the xml (mmp) file just saves the positions of the inputs (knobs) of the instrument plugin. If the instrument plugin doesn't have inputs for cutoff/frequency, there's nothing you can do (apart from implementing that functionality yourself and submitting a patch to git).
I think you can edit the XML, yes. You can also mess up, so have a backup.