Another option: Install his RootsMagic code on your computer. You use his registration. He uses your registration. License police are happy.
There is some obscure keystroke code using a combination of keystroke codes with maybe [ctrl] + [esc] + [alt] + [something else].
It resets RootsMagic and probably deletes the file association you carefully setup. And maybe something else.
However, I was not able to find it in the help files. It has been posted on this user site before. And whatever it is, I have never used it.
If you ever find it, make certain you have a good external backup first.
You have two licenses for your household and presumably two computers. Personally, I would not worry about it, but I do not create a RM website. Might make a difference.