Just case anyone else is looking for this, I found it in the view-functions.php. There are two lists for labels and values. If you want the selection box to show abbreviations, change the labels list. If you want to pass abbreviations to the database or to another form, change the values list. Or you can do both. Just keep in mind that when you update Machform, this will get overwritten so you'll need to change it again. (Saving and overwriting the new installation is NOT recommended)