Error Event Definition

Hi there,

Im using a modified version of the properties-panel example.
When you an error boundary event, it normally creates an in the bpmn and the code of that error is associated to the event in the field errorRef.
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Want i want to ask is how do i modify this in order for the errorRef being defined manually by the user?
Reason: the bpmn files are read by activiti (modified) and the errors given need to be only errors from our system (that will be listed to the user in bpmn-js in a select box).

Thanks!