Updating & creating issue with Redmine importer plugin

[Heremion]

Hi,

I actually use the redmine importer and i have some questions about it.

I would like to import in one shot a CSV file where some issues can already exist into my redmine database and some another not.
Could you tell me if it is possible to do that ?
In other way, do you have an idea to import issues knowing that into my CSV file, I can't identify issues which exist or not into my redmine database ?

Regards,