Hello Graeme Lynch,
You can disable the customize menu of a RadCommandBar
by subscribing and canceling the DropDownOpening
event of its menu:
sender, CancelEventArgs e)
As to the customize menu opening on a right click even on a command bar icon, this issue has appeared in the latest release and will be address in the upcoming SP1.
I hope you find this useful. Feel free to ask if you have any additional questions.
the Telerik team