I also had a real problem naming the "Store as" field for my data extractor. It didn't seem to like things in the format "foo_bar_baz56" (i.e. ending with digits). This page https://mrscraper.freshdesk.com/support/solutions/articles/1... says "The variable name can not contain special signs" but doesn't explain what special signs are. Anything other than [A-Z_]?
Now that I've finally set up and tested my first scraper, I'm really impressed. It was much easier to set up than I would have guessed, and specifying a selector made it dead simple. Results worked out of the box, on a site that is super touch about being scraped.
However, now that I'm viewing my scraper, I see no way of editing the scraper or data extractor. What's the trick to editing a scraper once you've saved it and gone back to view it?