In a Support discussion titled Splitting reply across two topics, Jonathan5 asks if it’s possible to split a single reply so part remains in the original topic and part becomes a new topic. EricGT, an admin, explains that Discourse currently lacks a clean one-step method for this. He recommends manually creating a new topic, copying the relevant portion, editing for clarity, and adjusting ownership — while deleting the moved portion from the original. He warns this can confuse users or feel like a violation of their content. His preferred solution is to privately message the original poster, asking them to split the reply themselves (or offering to do it for them), and suggests they edit the new topic’s title for accuracy. Jonathan5 agrees, noting he might add cross-links between posts and considers broadening the original topic title in ambiguous cases. He also proposes a feature enhancement: allowing the topic-split tool to leave the original post editable in the old topic, with automated clarity notes [4]. EricGT reframes this as reply splitting, not topic splitting, and suggests a future feature: a moderator-triggered canned message with embedded options to help users split replies themselves. Jonathan5 concludes that direct contact is best and appreciates the explanation.
Sometimes a reply is partly a good reply to the existing topic, but partly really a new topic starter entirely.
Is there any way of splitting part of this reply into a new topic but at the same time retaining the relevant part on the existing topic?
Thanks.
As someone with admin rights I know of no way to do this cleanly with one action.
AFAIK the easiest way to do this is to NOT split the topic using the split topic feature as that will move the entire reply which then leaves one with the undoable problem of trying to insert a reply in between replies.
Instead
For the new topic
a. Create a new topic
b. Copy part of the reply into the new topic
c. If needed, edit the wording so it makes sense.
d. Change the owner of the topic
For the existing topic
a. Delete the part of the topic moved.
b. If needed, edit the wording so it makes sense.
This also causes more problems because it confuses users and sometimes the creator of the reply sees it as a violation of their personal content and leaves them with a sense of distrust.
The better solutions I found is to just use a person-to-person message (private message) and ask the user to consider splitting off part of the reply into a new topic and note that you can do it for them if they request and that they can then edit both items as necessary. If I do the change I suggest that they edit the title of the new topic because what they intended is not always what the guessed title suggest.
Thanks. Your technical solution looks like it would work fine - I might also add links between the two posts - but I agree that it’s annoying to have your words mangled by someone else. With the reply that led to my query here, I think the answer might be to rename the topic to be broad enough for both “sub-topics”, but in a more black-and-white case I’d likely go down the personal route, as you suggest.
It would be nice if the topic-splitting feature would (or could) leave the original post in the old topic so that it could be edited. That way the automatic messages (small action posts?) about topic splitting would make the situation clearer.
Think about it for a minute. Is it really topic splitting? I would think of it as reply splitting.
However if one is seeking a new feature then I think what would be better is for a feature where a moderator uses the wrench to select the reply then chooses an option that sends a canned person-to-person message asking the user to split the reply and then the canned reply includes some options right in the message to help the user split the reply. 
I think your main solution is best – contact the person directly. I can see why it’s the way it is. Thanks!