macOS – Guide to Reinstall/Repair OS X without Losing Files

The preferences appear to be at: ~/Library/Preferences/com.apple.Terminal.plist

See also this question on SO and another question on SU that focus on exporting the settings from one Mac and moving them to another.

• https://stackoverflow.com/questions/8350065/
• http://superuser.com/questions/204686/

For older macOS, you can edit the file directly but on newer OS (with newer being 10.9 and later) you will want to use the defaults command to write the values to the persistent database (which may or may not flush back changes to the filesystem) rather than editing the file.

defaults read com.apple.Terminal

Or to write the secure keyboard entry function (as one easy example):

defaults write com.apple.Terminal SecureKeyboardEntry 1

Each Mac has a minimum build number that has the necessary drivers to run that Mac. Sometimes a build will run tens of Macs and some builds are very narrowly scoped to handle all the existing models and that one new release until those drivers can be incorporated into the next numbered release of the OS.

• Mac OS X versions (builds) for computers

What this means for you, is you'll need to try booting to the recovery HD on that SSD and hope the version of recovery is new enough to work to download he proper installer and let you proceed with the build for that Mac. If not, you'll need to place the drive that came with that Mini back in (or into an external USB enclosure that costs about $5 to $10 and hold the option key) to select that external drive.

At that point, you can re-run the installer or migrate the data from the SSD to the external drive. Then you can wipe the SSD clean using recovery and migrate back without having to reinstall or lose any data or settings.

There are many paths to getting back in business - but knowing the minimum builds will let you check things next time to run the updates before you move the drive.