Quote - Is this the only way to add to the runtime? I can't just copy it there?

Mac will not merge folders the same way that PCs do. If you try to do this it will ask if you want to replace the folder.

You can, however, manually copy the folders and files from the new runtime into their proper location in the target runtime folder.

"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)