I managed to import the blocklist from #TheBadSpace into my #GoToSocial instance but I had to tweak the CSV file a bit:
1. Open the CSV file with your favorite text editor
2. Add the `#` prefixe to all the columns on the first line
3. Open up the GoToSocial admin panel
4. Go to the Moderation > Federation > Import / Export section
5. Import the CSV file
6. Happily hit that submit button
Here's a visual diff for step 2: