Not necessarily. Consider products that require radios like satellite internet transceivers. If you were allowed to "modify it however you want" you could easily modify it to put up a continuous wave and effectively DoS the satellite gateway, causing an outage for all other customers on the entire beam which is obviously something the ISP wants to avoid at all costs.
Hence, many companies only allow you to lease the transceiver, not own. And even if you did literally own it, they obviously don't want you modifying it for fear of harming the service of other customers.
It's one thing if you buy a toaster and modify your toaster to burn cool patterns into your toast. It's quite another if you buy a toaster and modify your toaster such that nobody else's toaster in the neighborhood works anymore.