Multi Site Save Settings (feature request?)

I have been using this plugin successfully on a multisite installation and recently ran into a problem where a user on one site was overwritten by user on a different site. This was cause by the “new” user being assigned a user name the same as the existing user. I know that I can change the settings to prevent this from occurring but would like to save default settings to prevent this in the future.

On this multisite installation, websites are created for new customers. A template is provided so they may populate it with users, then import these users. There is no relationship or knowledge from one subsite user to another.

Might it be possible to do the following?
1. Administrator on main site of multisite installation can save default import settings that appear on all subsites.
2. Administrator on main site may select which import option settings are available on subsites (e.g. hide some options on subsites)

A possible method to do this:
Are there hooks available to use in my own plugin that would allow the the following on subsites?
1. Hide all fields (or choose which fields to hide). Desire is to hide fields between the CSV file chooser up to the Start Importing button.
2. Set the default Update existing users to No

Thanks,
Bill