Once a product is bought, the property changes of hands so this at a first glance doesn't have discussions. The warranty period is another matter, as it's more or less clear that some manufacturers prefer to not allow users opening the device in question. Anyway, it needs to be checked with some laws as some people should be allowed to open devices. With commercial intentions, several countries do establish penalties.
If you plan to customize your hardware with better pieces, or simply to avoid restrictions that cheat users subtracting characteristics that the device has, there's a possible limitation in terms of copyright, with registered software for services like decoding or in general that bypass commercial tariffs that others are legally paying.
Trying to impede the modification of analog circuits could be ridiculous, from technical service guys to users with interest on taking a soldering iron and do whatever they want with their device. The most cruel modification is when the device goes to the trash can and nobody thought about the recycling process but in making a profitable production.
There are multiple businesses that update analog circuits in lab, audio or video equipment. Sometimes there's some piece out of production and the only solution is to use other with better specifications to repair the product.
We think the law should protect the environment more establishing protocols to identify those lamentable tricks that some manufacturers engineer to make your product useless. Maybe forgetting some metal bolt, or a metal clip somewhere. This to avoid the incredible quantity of electronic waste that it produces day after day. The client-side modification, or say product rationalization, is an obligation here.
Do you have tools or knowledge for that? You should!