Hi LuisARG_Esri,
Instance of GeoEvent your processor receives from the event processing framework (EPF) is immutable because by default any processor IS NOT a GeoEvent Mutator. In order to change this behavior you need to override the following method inside of your processor code as follows:
public boolean isGeoEventMutator() { return true; }
This will tell EPF that your processor IS GeoEvent Mutator that should operate on its own instance of GeoEvent. EPF will cook it up for your processor and pass it in the [public GeoEvent process(GeoEvent geoEvent) throws Exception] method.
This should resolve the issue you reported.
Thanks,
Vlad Plechnoy.