After seeing this reddit post relating to a buttload being an actual medieval unit of measurement, I decided that I would update the units database on my machine. Here is the simple command that I came up with:
LOC=$(units -V | grep -o "[/a-z/]*\.dat"); echo "buttload winebutt" | sudo tee -a $LOC
It's simple enough, we get the location of the flat file database from the command's version output flag -v, then grep it to contain only the file name. Then, enter the new unit followed by a reference to an old unit. My up to date units database already had a winebutt defined, so I added the reference.
To add another unit, such as Schrute Bucks to Stanley Nickels we would say:
LOC=$(units -V | grep -o "[/a-z/]*\.dat"); echo "schrutebuck 50 stanleynickels" | sudo tee -a $LOC