TR Fuel lines and pressure regulators

Does anyone know if it's possible to yellow passivate (zink plate) these parts with the hard black plastic still attached? Or will the chemical process damage the plastic tubing?

I've taken it to my local metal finishers and he reckons it wont affect it and would try a small part to check first. Just wondered if anyone has already done it and knows whether it's possible or not?

Cheers

 

Thanks Jeff, i'll have him do a test on one first and if all goes well he can do the rest