Earlier, it used to be that companies such as Apple or car makers invoked copyright protection clauses in the old DMCA (Digital Millennium Copyright Act) and forbidding buyers from tinkering with the devices they bought. The whole idea of buying and owning something is being challenged nowadays.
On October 28, an exemption to the DMCA kicked in and now you can tinker without being sued by big business. However, the exemption is 'on trial' only and will be in efect for 2 years.
You should also remember that the onus is on the companies to prove that your modifications caused the malfunction.