Originally Posted by Schoenfeld
You are not opening up the source of what you've modified, and from what I see, you haven't registered a business.
To be fair, he may not need to register a business. It depends on the law in his country. Here in Denmark you do not need to register a business if your gross sales is below some well defined limit, and surely he would need to sell a serious amount of these devices before he would exceed that limit. He would still need to pay taxes obviously, but it would be his own responsibility to declare his earnings.
The rules may be different in Portugal, but due to the small size of this project, I don't think buyers should need to worry much about that.