Legality of Reverse Engineering
The best answer is always "talk to a lawyer."  That being said, you could check out any kind of license agreement you may have implicitly agreed to when you purchased the item.  Since you are not marketing this modification, the worst that could happen is that you could get a takedown request/notice for the video or a cease and desist letter.  Odds are, the company either will not care or will see this as free advertising.