It would be really helpful if open quotes were updateable. Adding a freebee or discounting a plan can help to close a sale but right now it means recreating the quote.
Thanks for writing in.
Any quote that is created is considered as an agreement with the customer and hence a change after the quote is generated is not allowed currently. Having said that, the ability to edit a quote has already been taken up as a feature request on our product roadmap and the feature is expected to be live by the end of January 2020.
That being said, we will try to release this earlier and keep you posted.
Also answered here- https://support.chargebee.com/a/forums/topics/328282