Do you mean the QAT?, The small Icons at top left, if so by clicking the down arrow you can add to it, you can choose more commands which will open up a dialogue box with more choices. By right clicking anything in the ribbon you can add it to the QAT.
Not sure if it's a rhetoric question, but the page where you picked the picture from clearly mentions that it's 'nearly' impossible. I am not sure if the writer just didn't want to completely dishearten a persistent developer, or whether s/he didn't have cent per cent faith in self, but I'd be happy to keep an eye on this thread and see if it's possible at all.
I had seen the article that Sam posted, but not the other one. However, both of these articles describe customizing the Context Menu and not the Mini Toolbar. One of my goals is to make Excel easier/simpler to use, so I wanted to eliminate several of the choices in the Mini Toolbar that are seldom used. I use Custom Ribbons and have found some "secrets" that make life much easier for me and many others that I've shared these with. I wanted to try to expand that to other areas in Excel and thought the Mini Toolbars were ripe for picking. But alas, it may not be.
Hi, Ronald Wilson!
Sorry to say but I'm bad news... unless you want to get your hands dirty with VBA code particularly not so simple. But as you asked, here's what the geniuses of the Redmond guys officially stated about customization of contextual menus, aka right click menus... unless you're left-handed and had a mouse configured as you should. http://msdn.microsoft.com/en-us/library/gg469862(v=office.14).aspx
Regards!
PS: And it's free! :D