Do you already have the security groups defined in both environments?
When you export a role you can either import this into an existing role, or create a new role and import it into a new role so that the permission changes take place.
When you import a role into another role, this WILL overwrite permissions.
Take the backup of security permissions of existing group in production server of particular group and import the new permissions to override the existing. But make sure that you are importing the group which you have taken the backup and check the security permissions. Mostly there will be no problem and in the worst case if any problem comes have to revert back.