Google is taking a while to re-index changes I have made to thousands of pages, so I want to use Fetch as Google to give it a prompt. However, you can only enter 1 URL at a time as standard.
Is there a way to bulk submit URLs to it?
Create a page with links to all the URLs you'd like re-crawled (like a sitemap) and add that to your website.*
Submit the URL to that page to Fetch as Google, selecting Desktop as the fetching strategy, as detailed here: Use Fetch as Google.
Once Fetch as Google is complete, and within 4 hours time, from the Fetches Table next to the status of the fetch, select Submit to Index, then select Crawl this URL and its direct links, followed by Submit.
As indicated in Ask Google to re-crawl your URLs, the above will:
Submit the URL as well as all the other pages that URL links to for re-crawling. You can submit up to 10 of requests of this kind per month.
*As commented by John Mueller, you can also submit a sitemap file or a text file containing a list of URLs.