If you like what you see, go right ahead and install it on your regular startup volume. As were the last few versions of OS X, Yosemite is available from the Mac App Store. To get your copy select ...

From there, you should see OS X Lion as one of your previous purchases. Click the Download button next to Lion, note the directory that it downloads to and wait for the download to finish.

and see what scripts an installer will run. The macOS installer architecture is very robust and in fact goes all the way back to the very first release of Mac OS X in 2000. Actually, the .pkg ...