Introducing displaced vertex for Pythia event

Dear All,

I am trying to let a Pythia particle decay away from the centre of a detector i.e. at a displaced vertex position.
By default the particle_position=(0,0,0) in the source code of G4HEPEvtInterface below :
G4PrimaryVertex* vertex = new G4PrimaryVertex(particle_position,particle_time);
and I want to make it e.g., particle_position=(10,10,10) in for Pythia events.

Can anyone suggest me how this can be acieved?

Thank you,