sure, I actually just added this filter to the query I am using myself last night and was going to include it in a future update to this post. To exclude something we will use the "NOT" operator: add this in after the WHERE statement:

NOT category IN ('introduceyourself', 'cn', 'meme', 'christianity', 'religion', 'god', 'bible', 'aceh', 'introducemyself') and

above I have excluded categories that are not allowed in the guidelines (introduceyourself/myself and religious posts) as well as cn and aceh (mostly foreign language posts) and meme (mostly memes LOL). You can add others to exclude of course but I found that just excluding these already made a big difference as far as getting rid of chaff in the search results. Thanks for the question and I am glad you were able to follow my instructions and run the query! Cheers - Carl
to add more categories to exclude just make sure to enclose them in single quotes (example: 'categoryname') and to include a comma after each category except the very last one before the closing parenthesis.