You can disable certain entries in the global settings page of the VM selector:

$ VBoxManage setextradata global GUI/RestrictedGlobalSettingsPages property[,property...]

property is one of the following:

General

Do not show the General settings pane.

Input

Do not show the Input settings pane.

Update

Do not show the Update settings pane.

Language

Do not show the Language settings pane.

Display

Do not show the Display settings pane.

Network

Do not show the Network settings pane.

Extensions

Do not show the Extensions settings pane.

Proxy

Do not show the Proxy settings pane.

This is a global setting. You can specify any combination of properties. To restore the default behavior, use the following command:

$ VBoxManage setextradata global GUI/RestrictedGlobalSettingsPages