Is it possible to customize the Rich Text Editor toolbar for a particular field? For example, remove a toolbar or a button?
Yes, this can be done by using the Source of an Html field.
You can remove buttons in the same manner.
Save the template.
Use the template you've just edited to create a new Item in the Content Editor. The Item will contain an html field.
Click on the Zoom button of this field and you will see that only two toolbars are displayed:
You can remove buttons in the same manner.