No, that won't work on a Mac (I have a Mac too).
On a Mac, this won't merge the runtime, but it will ask you if you want to replace the runtime with the new one. Of course, you don't!

I use a utility called dittoGui to merge a new runtime into an existing library.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)