I have tried to update the forum topic as below,

EPiServer.Community.Forum.Topic topic = GetTopic();
EPiServer.Community.Forum.Topic topicClone = topic.CreateWritableClone() as EPiServer.Community.Forum.Topic;

UpdateForumTopic(topicClone);// Edit the forum topic (e.g. change body text etc.) 

topicClone.Changed = topic.Changed; // This could not be done as there is no setter
EPiServer.Community.Forum.ForumHandler.Instance.UpdateTopic(topicClone); // Updating the forum topic will set the Changed state to true

However, I need to preserve the Changed state as it is even after updating the forum topic. Is there a way to do that?

Additional info on my setup:

EPiServer.Community -  version=9.0.0
EPiServer.CommonFramework - version=9.0.1