Legal Question in Intellectual Property in California

Yes. Altering a trademarked product falls under the legal heading of "trademark dilution," which means, in general terms, that the right of the trademark owner to be sure that its products reach the ultimate consumer in its as-intended condition (quality, integrity, consistency of design, consumer expectations in all regards, etc. etc.) is infringed by such modifications.

You can't buy a Ford, put a Chevy engine in it, then sell it as a Ford.

Similarly, trademark law includes the right of the trademark owner to be certain that goods sold under its trademark are essentially un-altered -- whether the alteration is an improvement or not, or is fully known by the consumer/buyer at the time of purchase, notwithstanding.