Hi @Dennio! A warm welcome to the land of Zynthian.
Yes, you can use webconf to do this. Navigate to INTERFACE->MIDI OPTIONS then enbale “Advanced view”. This exposes the “MIDI filter rules”. Add a rule for each MIDI note you wish to map and remember to add a pair of rules, one for NOTE ON and another for NOTE OFF. For example the following rule will remap MIDI note 60 (middle C) to note 62 (D) on MIDI channel 1:
MAP CH#0 NON#60 => CH#0 NON#62
MAP CH#0 NOFF#60 => CH#0 NOFF#62
It does not unmap note 62 so pressing and holding C then pressing and releasing D will stop the original note playing.