First, AutoCorrect and a dictionary file are different things.
See
Mastering the Spelling Checker by Suzanne Barnhill, MVP.
How is your custom dictionary file constructed. I haven't looked into them for more than a decade. My recollection is that such files are simple text lists of words that are in alphabetical order and to which a .dic filename extension is applied. Again, they have nothing to do with AutoCorrect really.
It is possible to add things to AutoCorrect in bulk as well.