So I was forced to install the OWC SSD first. As you power up the computer, press the CMD + R keys to access the disk recovery menu. That allows you to choose the internal drive for the OS X download. But, a funny thing happened. Apple would only allow me to download Yosemite onto the new drive. So, Yosemite came first, then came the upgrade to El Capitan, which took an additional 20 minutes.
Now that you've got OS X El Capitan on your OCW SSD, you'll need to migrate the data from your original SSD. There are several ways to do this.
You can use an updated Time Machine backup, but I prefer to simply insert the factory SSD into the OWC adapter, plug it into the USB port and then go into the Utilities folder and select the Migration Assistant. After that, it's just a matter of selecting the source drive (your factory SSD connected via the USB 3.0 cable) and the target drive, your new OWC SSD.
I had 240GB worth of data to migrate, the process took about 45 minutes.
I can't emphasize enough what a relief it was to avoid having to dump data off my old drive in order to free up space. With the new 1TB Aura SSD, I've got plenty of breathing room for years to come. And, if I ever decide to get a new laptop, my mid-2013 MacBook Pro will have at least as good an SSD as Apple is likely to offer any time soon.
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