Well apparently I was wrong about the API limit, as I started getting 429 errors ("Too Many Requests") after around ~6500 tag changes.
Still, my user JSON page still shows that I have used no API requests, either read or write. So it looks like that the restriction is in place and working, but the information about that from the user page is incorrect...?
{"id":23799,"name":"BrokenEagle98","level":32,"inviter_id":13392,"created_at":"2007-12-31T04:13:18.602Z","base_upload_limit":50,"post_update_count":149496,"note_update_count":24233,"post_upload_count":6699,"wiki_page_version_count":1937,"artist_version_count":3896,"artist_commentary_version_count":1436,"pool_version_count":1397,"forum_post_count":1060,"comment_count":1360,"appeal_count":4,"flag_count":30,"positive_feedback_count":10,"neutral_feedback_count":1,"negative_feedback_count":1,"is_banned":false,"can_approve_posts":false,"can_upload_free":true,"is_super_voter":false,"level_string":"Builder","remaining_api_hourly_limit":50000,"remaining_api_hourly_limit_read":50000,"remaining_api_hourly_limit_write":5000}
Can someone else confirm this...? If the above is true, then an issue should be submitted for it, since otherwise I'll have to have my script blindly guess when it's okay to start tagging again... :/
Edit:
Or maybe not... after letting it rest for a couple of minutes and restarting it, it's going at full speed again, so... ¯\_(ツ)_/¯