A few weeks ago I swapped the hard disk drive in a 2012 Macbook Pro with an SSD. It’s worked really well; the laptop runs faster than I have ever seen it, and it’s easily added 3 or 5 more years to the laptop’s life. If you have one of these old pre-retina Pros, I highly recommend it.
The process, including the macOS re-install and data restore, took about 4 hours. The actual disk swap took no more than 30 minutes; it’s not very difficult as long as you are careful:
I created a macOS Sierra installer USB pen drive on my own MacBook Air.
In parallel, I created a Time Machine backup of the MacBook Pro (which ran Yosemite) on another disk.
Opened the MacBook, swapped the drives, reattached the bottom panel as in the guide. Here is the machine with the drive in:
Then booted from the USB pen drive (hold down the Alt/Option key when booting). In the installer, used Disk Utility to erase the SSD and create a HFS+ partition. Then installed Sierra on it
During the installation, was asked if I wanted to restore from a Time Machine backup, and used the one I had created earlier.
Boom. MacBook Pro has new lease of life.
PS: The machine had 8GB RAM and a 2.6GHz processor. It’s a rather powerful machine let down terribly by its hard drive.