The need to do this hasn't arisen often, but it does arise.
I am quite familiar with the merge feature on groups.io, but I don't see any explicit function that allows you to split a post (or series of posts) contained in an existing topic off into a new topic of their own, usually assigning a new topic title as part of the process.
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Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
???? I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.
? ? ? ? ?~ Galileo Galilei