itch.io have specifically requested that people do NOT use such tools as it hammers their server and is similar to a denial-of-service attack! They have said they will provide an "Add all games" button once things have settled down for them and they get the chance to do it.
If you want to be more selective in adding games, I'd recommend the https://randombundlegame.com/browse website. If you provide it your download link you can use it individually register games for you easily.