I did this with Python in case anyone was looking.
All you have to do is download the .crx file (I used https://chrome-extension-downloader.com/) and save it somewhere that Python can access it. In my example, I imported it to the same folder as my Python script, to load exampleOfExtensionDownloadedToFolder.crx.
from selenium import webdriver
from selenium.webdriver.chrome.options import Options
options = webdriver.ChromeOptions()
options.add_extension('./exampleOfExtensionDownloadedToFolder.crx')
driver = webdriver.Chrome(options=options)
driver.get('http://www.google.com')