Hi Jordi,
Thanks again for bringing this up. I spoke to the team yesterday and confirmed that we do currently go through the review process for deploy percentage changes via. the API.
Our documentation is wrong there, so I'm working on updating it.
It also doesn't seem like ideal behavior - so we are having some discussions about if we can change this or potentially add a new API endpoint to match the behavior in the UI.
Apologies for the trouble.