Apple - Import keychain to clean macOS install?

Actually that is pretty easy and a common question out there on the internet. OSXDaily says this is the best way to copy a keychain to a new Mac.

1. From the Mac OS X Finder of the Mac containing the original keychain file, hit Command+Shift+G to bring up Go To Folder and enter the following path:

   ~/Library/Keychains/
   

2. Copy the user “login.keychain” file to the new Mac, do this with AirDrop, Ethernet, USB, etc

3. On the new Mac, hit Command+Spacebar to open Spotlight and type “Keychain Access” then hit return, this launches the Keychain manager app
4. Pull down the “File” menu and select “Add Keychain” and browse to the keychain file you copied to the new Mac, selecting Add to import the stored keychain data to the new Mac.

Sounds about right to me.

In addition to @SteveChambers' answer from the looks of it you could import the contents of the old keychain into your existing keychain's file as well.

This Apple doc covers this: Keychain for Mac: Import and export keychain items.

You can do so under the Keychain app's menu (File → Import Items). Additionally I believe you can open up the 2 keychain files and drag items from one to the other as well.

References

• Q: Keychain Access - Easiest way to move data to new machine?