it's a one-time only thing. i was trying this four times by now, starting in my previous save. i think that was just a glitch maybe based on my own unity installation? or visual studios or what ever.
An unofficial one but yes, there is! https://john-games.itch.io/unofficial-autonauts-level-editor
Thanks for helping everyone out on Itch btw! If you want you could join our Discord server and speak to others about Autonauts :)