I don't have first hand experience with PowerCMS but most applications based on this editor control the options by editing the .js file. All I do is make a backup of the file and delete the buttons I don't want. If you look at how they are grouped, it pretty easy to understand the syntax. Just make sure you keep the punctuation intact. If you don't get what you want, you can just copy the backup file on top of the modified one and start again.