ps. Sorry, the icons on the main toolbar are fixed and permanent, otherwise people (other than you) mess with the toolbar and then ask where the buttons have gone.
Ideally the solution would be to hide the main toolbar and configure the custom toolbar to have only the buttons you want, but unfortunately the user-defined tool icons only get added to the main toolbar which would defeat what you are trying to achieve.
So in 7.3 I'll check for the main toolbar being invisible and the custom toolbar being visible and then add the user-defined tools to the custom toolbar.