Well, i'd like to do an automatization to edit a thread in a certain amount of time with a program. I really don't know how to do it, i don't even know if it's possible to do without an API. It's feasible without an API?
If you are asking that if you can add a thread to a forum post using qt. Well that is possible if the forum doesn't have captcha or other protection mechanism against posting.
What you will need to to is inspect the login sequence and the post of the forum using fiddler and then develop qt code that will replicate the same.
But is complicated for a beginner.I suggest you learn how to make POST and GET request using Qt and then start developing an automatic forum poster.
Hope it helps