The easy, but sort of hackish way would be to pre-install Opera as USB standalone, set it up there and then distribute such package to all users in the environment, but I understand you need a solution which involves all users' or current user installation?
Thanks Idrin. You are right, I need a standard way of managing the deployments and/or configuration. It doesn't necessarily need to be at the time of installation, it could be at user profile creation like an active setup.
Is there any documentation I've missed on what the pref_default_overrides or other files do, or how to use them?