It sure would be nice to have the ability to update conditional formatting via the API. I see a thread from 2016 - is this something that the dev team could look at?
When you have a moment, please submit a product enhancement request using the form under Quick links on the right to let our Product team know that you'd like to have this functionality in Smartsheet.
I agree that this would be a really useful feature. I have submitted an enhancement request for this. Additionally as Sean pointed out in the post above, this was first requested back in 2016. It has been 2 1/2 years since Sean's post. It would be great if this useful feature could be lifted to the API.