After I posted my question on the undocumented grip change for the Wacom Intuos4 pen, my Youtube buddy CyberLCF came up with a video he found to bring light into the darkness.
As you can see you can easily pry out the buttons (this was something I was concerned about) and then disassemble the pen. Then just pull it out of the original grip and place the optional grip on it. Assemble it again and you are done.
Of course I tried it and found it obsolete to make a video of it. Besides this I decided to use the original grip. However, if something is possible I want to know how it works.
Have a great day!