I confess I’ve never played this “card” in nearly 50 years of practice, but in virtually every State I’m familiar with the definition of the practice of professional engineering includes
judgement as well as simple compliance with Codes and Standards. See the Code of Ethics section in
New York – Laws, Rules and Ethics for Professional Engineers. [Paragraph II.1.1] (You probably should read the whole thing)
California is fairly specific:
6703. Responsible charge of work defined
The phrase “responsible charge of work” means the independent control and direction, by the use of initiative, skill, and independent judgment, of the investigation or design of professional engineering work or the direct engineering control of such projects. The phrase does not refer to the concept of financial liability.
Oddly enough, NFPA 54 says: Piping shall be anchored to prevent undue strains on connected appliances and equipment and shall not be supported by other piping. Similarly, like NEC Section 300.11, I can't find a specific prohibition, but it's hard to think prohibiting supporting other piping but permitting support for a foreign system would be acceptable.
This is all to say that if you are uncomfortable with it, don't do it.