thanks @Mighty23 & @aaronventure !

Success 😍

It seems to matter that:

the original script node containing the faust dsp needs to be deleted, not just 'switched' off. in hardcodedMasterFX the scriptnode needs to be selected. (in the case above scrip_fx1, not 'minimalGain'.)

It's a bit tricky. Thanks a lot!
Moving on... ;)