Can you add a 20/50 oil to 4 qts. of 10/40 when changing the oil? 225k miles.

What is your question?

A mechanic said he adds 1 qt. of 20/50 to 10/40 when he changes oil. I asked about the "no Zink" in the new oil not good for older engines. I've used 10/40 for many years, now. Do you think this is a good idea?